Sustained release system for reservoir treatment and monitoring

ABSTRACT

Compositions containing a mixture of microcapsules and a bulk polymer, where the microcapsules have an oil field chemical contained within the microcapsules are provided. The microcapsules can be present in a variety of configurations. The microcapsules contain a core or a micro-matrix containing the oil field chemicals. The core or micro-matrix can be surrounded by one or more polymeric shells, where each shell contains at least one polymer that affects the release of the oil field chemical from the composition. The compositions provide for the sustained release of an oil field chemical into fluid in an oil field reservoir over long periods of time. Methods of making the compositions and articles containing the compositions are also provided. Further provided are methods of tracing the movement of fluid in a hydrocarbon reservoir using the compositions, and methods of providing for the sustained release of oil field chemicals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International PatentApplication No. PCT/GB2016/051172 filed Apr. 26, 2016, which claimspriority from Great Britain Patent Application No. 1507479.2 filed Apr.30, 2015, the disclosures of each of which are incorporated herein byreference in their entireties for any and all purposes.

FIELD OF THE INVENTION

The present invention is directed towards compositions comprising amixture of a bulk polymer with microcapsules containing one or more oilfield chemicals within the microcapsules. Articles comprisingmicrocapsules incorporated into a continuous bulk polymer matrix canprovide for the sustained release of the oil field chemical into oilfield fluids over periods of time from weeks to years.

BACKGROUND OF THE INVENTION

It is common practice to deliver oilfield chemicals to a subterraneanhydrocarbon reservoir to bring about a variety of functions at variousstages of hydrocarbon production. Examples of oil field chemicals arescale inhibitors, hydrate inhibitors, corrosion inhibitors, biocides,and wax and asphaltene control substances.

Oilfield fluids are complex mixtures of aliphatic hydrocarbons,aromatics, hetero-atomic molecules, anionic and cationic salts, acids,sands, silts, clays and a vast array of other components. The nature ofthese fluids, combined with the severe conditions of heat, pressure, andturbulence to which they are often subjected during retrieval, arecontributory factors to paraffin deposition (including the precipitationof wax crystals), emulsification (both water-in-oil and oil-in-water),gas hydrate formation, corrosion and asphaltene precipitation in oiland/or gas production wells and surface equipment. This, in turn,decreases permeability of the subterranean formation, reduces wellproductivity and shortens the lifetime of production equipment. In orderto remove such unwanted deposits and precipitates from wells andequipment, it is necessary to stop the production which is bothtime-consuming and costly.

Further examples of oil field chemicals are thickeners and gel breakersused in hydraulic fracturing. Hydraulic fracturing is a well-establishedtechnique for stimulating production from a hydrocarbon reservoir. In aconventional fracturing procedure, a thickened aqueous fracturing fluidis pumped into the reservoir formation through a wellbore and opens afracture in the formation. Thickened fluid is then also used to carry aparticulate proppant into the fracture. Once the fracture has been madeand packed with proppant, pumping is stopped. The formation closes ontothe proppant pack and oil or gas can flow through the proppant pack tothe wellbore. At least some of the aqueous fracturing fluid in thewellbore will be driven back to the surface by fluid produced from thereservoir. The fracturing fluid is subsequently pumped out andhydrocarbon production is resumed. As the fracturing fluid encountersthe porous reservoir formation, a filter cake of solids from thefracturing fluid builds up on the surface of the rock constituting theformation. A thickener, which increases the viscosity of the fracturingfluid, can be a polysaccharide. Guar gum, often cross-linked with borateor a zirconium compound, is frequently used. Another category ofthickeners which are used are viscoelastic surfactants. An oilfieldchemical can be delivered to a reservoir during fracturing. If thefracturing fluid contains a viscosifying thickener, it is normal tosupply a so-called breaker (which is usually an oxidizing agent, an acidor an enzyme) into the fracture to degrade the thickener and so reducethe viscosity of the fluid in the fracture after it has served itspurpose. This facilitates the flow back to the surface and the flow ofproduced fluid through the proppant pack towards the wellbore.

A further example of an oil field chemical is chemical tracers used formonitoring of hydrocarbon reservoirs.

Optimal oil production from the reservoir depends upon reliableknowledge of the reservoir characteristics. Traditional methods forreservoir monitoring include seismic log interpretation, well pressuretesting, production fluid analysis, production history matching andinterwell tracer techniques. Due to the complexity of the reservoir, allinformation available is valuable in order to give the operator the bestpossible knowledge about the dynamics in the reservoir. One commonsecondary oil recovery process is water injection in dedicated injectionwells. The water may travel in different layers and sweep (flow across)different areas in the reservoir. Monitoring of the production of thiswater in different zones in the well is important to design a productionprogram that improves the sweep efficiency and thereby increase oilrecovery. Mixing of injection water and formation water originallypresent in the reservoir may cause supersaturated solutions leading toprecipitation of particles (scale) in either the reservoir near-wellzone or in the production tubing. By knowing which zone or zonescontribute to water production, action can be taken to reduce the effectof scaling and thereby maintain productivity.

The use of tracers to obtain information about a hydrocarbon reservoirand/or about what is taking place therein has been practiced for severaldecades and has been described in numerous documents. Tracers haveprimarily been used to monitor fluid paths and velocities. More than onetracer substance can be used concurrently. For instance, U.S. Pat. No.5,892,147 discloses a procedure in which different tracers are placed atrespective locations along the length of a well penetrating a reservoir.The tracers are placed at these locations during completion of the wellbefore production begins. The tracer at each location is either attachedto a section of pipe before it is placed at that location or isdelivered into the location while perforating casing at that location.When production begins, monitoring the proportions of the individualtracers in the oil or gas produced by the well permits calculation ofthe proportions of oil or gas being produced from different zones of thereservoir.

Tracers have been used in connection with hydraulic fracturing, mainlyto provide information on the location and orientation of the fracture.Tracers can also be used for estimating residual oil saturation. Tracershave been used in single well tests and in interwell tests. In singlewell tests, a tracer is injected into the formation from a well and thenproduced out of the same well mixed with fluids from the well. The delayin time needed to return to the ground between a tracer that does notreact with the formation (a conservative tracer) and one that does (apartitioning tracer) will give an indication of residual oil saturation,a piece of information that is difficult to acquire by other means. Ininterwell tests, the tracer is injected at one well along with a carrierfluid, such as water in a waterflood, and detected at a producing wellafter some period of time, which can range from days to years.

Radioactive and chemical tracers have been used extensively in the oilindustry and hydrology testing for decades. Non-radioactive chemicaltracers offer distinct advantages over the use of radioactive tracers.For example, there are more unique chemical tracers than radioactivetracers and no downhole logging tools are required.

Oilfield chemicals are normally formulated with adjuvant or carrierchemicals before being introduced into a reservoir. When the formulatedmaterial is a liquid, the liquid can be pumped down a wellbore to thereservoir. When the formulated material is a solid, it can be pre-placedonto equipment, such as the well bore, before the equipment is placed inthe well. Particles of the oil field chemicals may be absorbed into thepores of porous carrier particles or encapsulated in a structure inwhich the oilfield chemical is enclosed within a shell of carriermaterial around the oil field chemical, and the particles are suspendedin a fluid and pumped downhole into the reservoir.

Despite the very wide usage of oil field chemicals, many of the currentmethods of introducing and using these chemicals have disadvantages.

One issue is the difficulty in handling oilfield chemicals that are indifferent physical states. For example, when different tracers areplaced at their respective locations along the length of a wellpenetrating a reservoir, a stable solid form of a tracer formulation isnormally used. Compared to solid tracers, tracers in liquid and gas formare often difficult to formulate and shape into stable solid objects.This can limit the types of tracers that can be used.

Another issue is that some oil field chemicals are reactive, making themdifficult to formulate and deliver into the reservoir.

A further issue is that unwanted inhomogeneous compositions can resultfrom formulating some oil field chemicals. This is found when attemptingto formulate different tracers with polymers to form objects forapplication to hydrocarbon reservoirs. Tracers can differ from eachother with respect to a variety of properties, such as density, particlesize, and in various surface related properties. These differences canbe very significant. For example, it is known that the density of oiltracers can vary from 1 to 3 g/cm³ and these differences can result invarious problems. The differences between the densities of the tracerscan result in compositions comprising a tracer and polymer havingsignificant non-homogeneous structure and morphology. High densitytracers tend to settle during the formulation process used to form thetracers into objects. Such non-homogeneous objects tend to showundesired release behavior in a subterranean reservoir environment.Although the use of an extra dispersing/stabilizing additive in theformulation of the objects can partially alleviate this problem, otherassociated problems, such as poor mechanical strength in a reservoirenvironment, remain. As a result, sometimes even apparently similartracers in one family cannot be formulated in the same way.

One of the most important issues is the release of oil field chemicalsfrom formulated articles to the targeted fluid or reservoir areas. Whileit is often a requirement for oil field chemicals to be released in asustained manner, e.g. slowly so that treatment can be effective overlong periods of time (e.g., years), the release of the chemicals incurrent commercial practice is often too fast (less than 6 months) andnot up to the needs of the industry. As a result, some oil fieldchemicals have to be repeatedly introduced into wells to ensure that therequisite level of the well treatment agent is continuously present inthe well. The release of oil field chemicals, such as tracers, is oftennot controlled in current practice, causing significant variations overtime for both a single tracer and as well as between different tracers.Such issues often result in ineffective treatments or loss of monitoringof the reservoir, and result in lost production revenue due to down timeand the costs of the additional materials that are used retreat thewells.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above mentionedissues related to the delivery and release of oil field chemicals. Oneadvantage of this invention is that it provides a means to process,deliver and release oil field chemicals, such as tracers, that can be insolid, liquid or gaseous form. Another advantage of this invention isthat it provides a means to overcome problems associated with the use ofmore than one oil field chemical (e.g. tracers, biocides) in acomposition and provides compositions having more uniform macrodimensions. The compositions described herein allow liquid, solid andeven gaseous oil field chemicals to be used and also minimize theeffects of using oil fields chemicals having different properties (e.g.densities). It is most advantageous that the present invention providescompositions and articles that allow oil field chemicals to be releasedin a sustained way over a long period of time that is closer to the lifeof an oil well than what is found in currently used compositions. It isa further advantage of the present invention that the release rate ofoil field chemicals is controllable and in some aspects of the presentinvention, the release rate of oil field chemicals, such as tracers, canbe relatively constant over a long period of time. As a result, thepresent invention provides ways to easily formulate and deliver oilfield chemicals, such as tracers, biocides, scale inhibitors, etc., to ahydrocarbon reservoir, as well as methods to monitor and trace the flowof fluids in a hydrocarbon reservoir.

In the first aspect of the invention, a composition comprises (a)microcapsules comprising an oil field chemical and a microencapsulant,where the microcapsules have an outer surface, and the oil fieldcompound is contained within the microcapsules and (b) a bulk polymer,where the microcapsules are embedded within the bulk polymer. Themicrocapsules can have a variety of structures, as described herein. Thecomposition can be in the form of an article configured for placement ina hydrocarbon reservoir. The composition can provide for the release ofan oil field chemical such that various amounts of the oil fieldchemical can be released over various lengths of time.

In another aspect of the invention, a hydrocarbon reservoir monitoringsystem comprises a composition of the first aspect of the invention.

In still another aspect of the invention, methods of making thecompositions and articles described herein comprise: (a) providing aplurality of microcapsules, each microcapsule comprising an oil fieldcompound and a polymeric microencapsulant, where the microcapsulecomprises a core shell structure, a core multishell structure, amulti-core shell structure, a micro-matrix structure, a micro-matrixwith shell structure or a multi-core-micro-matrix with shell structure,and (b) embedding the microcapsule particles with a bulk polymer

In yet another aspect of the invention, methods for providing for theslow release of an oil field chemical into a well or hydrocarbonreservoir comprises placing within a well or reservoir a composition ofthe first aspect of the invention where the oil field chemical is a welltreatment agent.

In yet another aspect of the invention, methods for tracing fluid flowfrom a hydrocarbon reservoir comprises the steps of placing within awell penetrating said reservoir a composition of the first aspect of theinvention, where the oil field chemical is a tracer, collecting one ormore samples of fluids flowing from the well and analysing said sampleto determine: (a) the presence or absence of the tracer or (b) theconcentration of one or more tracers in fluids flowing from the well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood from the following detailed descriptionwhen read in connection with the accompanying drawings.

FIGS. 1A-1F are representations of the structures of differentconfigurations of microcapsules.

FIG. 2 is a graphical representation of the dissolution rate of a tracerinto an eluent and the release rate of a tracer from microcapsules intoan eluent.

FIG. 3 is a graphical representation of the release rate of an aromatictracer into toluene from (a) microcapsules incorporated into epoxy resinas described in Examples 1-2-3, (b) pure tracer incorporated into epoxyresin as described in Comparative Examples 1-2 and (c) pure tracer alongwith fumed silica incorporated into epoxy resin as described inComparative Examples 3-4.

FIG. 4 is a graphical representation of the release rate of an aromaticketone tracer into synthetic oil from (a) microcapsules incorporatedinto a bulk polymer (polybutylene terephthalate (PBT)) as described inExamples 4-5-6, (b) pure tracer incorporated into PBT as describedComparative Examples 5-6.

FIG. 5 is a graphical representation of the release rate of an aromatictracer into synthetic oil from (a) microcapsules incorporated into abulk polymer (Polypropylene (PP)) and from a mixture of the tracer inthe bulk polymer as described in Example 7-8-9, (b) pure tracerincorporated into PP as described in Comparative Examples 7-8.

FIG. 6 is a graphical representation of the release rate of an aromatictracer into synthetic oil from microcapsules incorporated into a bulkpolymer (epoxy resin) as described in Example 10.

FIG. 7 is a graphical representation of the release rate of an aromatictracer (tracer B) into synthetic oil at 90° C. from microcapsules in abulk polymer (epoxy resin) as described in Example 15 and 17.

FIG. 8 is a graphical representation of the release rate of an aromatictracer (tracer A) into toluene at 60° C. from microcapsules in a bulkpolymer (epoxy resin) in an extended period between 4000 and 17000 hoursas described in Example 1, 2, 3, and 18.

FIG. 9 is a graphical representation of the release rate of an aromatictracer (tracer E) into synthetic oil at 90° C. from microcapsules in abulk polymer (epoxy resin) as described in Example 19, 20 and 23.

FIG. 10 is a graphical representation of the release rates of anaromatic tracer (tracer E) into synthetic oil at 90° C. frommicrocapsules in formulated bulk polymers (2 formulated epoxy resins: Iand II) as described in Example 19, 21, 22, 24 and 25.

FIG. 11 is a graphical representation of the release rate of an aromatictracer (tracer B) from pure tracer in a bulk polymer (epoxy resin) intosynthetic oil at 90° C. as described in Comparative Example 9 and 13.

FIG. 12 is a graphical representation of the release rate of an aromatictracer (tracer E) from pure tracer in a bulk polymer (epoxy resin) intosynthetic oil at 90° C. as described in Comparative Example 14 and 15.

DETAILED DESCRIPTION OF THE INVENTION

The inventors have surprisingly discovered that compositions andarticles having the structures described herein provide a means for thesustained release of compounds under conditions simulating those foundin hydrocarbon reservoirs. By microencapsulating an oil field chemicalinto a microcapsule, incorporating the microcapsule into a bulk polymerto form a mixture and then forming an article from the mixture, thearticle provides for a much slower release than is observed from eithersimply incorporating an oil field chemical into a liquid or a bulkpolymer, or just incorporating an oil field chemical into amicrocapsule. The microcapsule and the bulk polymer in the compositionappear to work synergistically so that the reduction of the release rateof the oil field chemicals from the composition is much greater thanexpected from simple combination of the two components as barriers. Themethods and processes described herein can overcome difficulties inmaking compositions comprising oil field chemicals (e.g. tracers,biocides, scale inhibitors) having different properties. Thecompositions can be macroscopically uniform throughout, independent ofthe oil field chemical selected. Liquid, solid and even gas oil fieldchemicals can be processed by the methods described herein to form thesame types of controlled release compositions. Applications of thecompositions and articles to hydrocarbons reservoirs or wells provideways to treat hydrocarbon reservoirs and ways to monitor and trace theflow of fluids in the hydrocarbon reservoirs.

The following definitions are provided in order to aid those skilled inthe art in understanding the detailed description of the presentinvention.

As used in this specification and the appended claims, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly indicates otherwise. Thus, for example, reference to “amicrocapsule” includes a mixture of two or more microcapsules, unlessspecifically stated otherwise.

As used herein, the term “about” means approximately and refers to arange that is ±25%, preferably ±10%, more preferably, ±5%, or mostpreferably ±1% of the value with which the term is associated.

When a range, or ranges, for various numerical elements are provided,the range, or ranges, includes the end values, unless otherwisespecified.

The term “release” means a process where one or more compoundsintroduced to a subterranean hydrocarbon (oil or gas) reservoir or wellin the form of a composition or an article move from the composition orarticle into one or more fluids in the reservoir. The term “release”,when used in the context of laboratory testing, refers to the movementof one or more compounds from a composition or article into an eluentthat is representative of a fluid in the reservoir.

The term “sustained release” means a process whereby one or morecompounds are released from a composition or an article and move fromthe composition or article into one or more fluids in a subterraneanhydrocarbon (oil or gas) reservoir or well over a period of time frommore than 24 hours, preferably more than 6 months, more preferably morethan 1 year, even more preferably more than 5 years, to more than 20years.

The term “oil field chemical” means one or more chemical compounds ormixtures that can be released into a subterranean hydrocarbon (oil orgas) reservoir or well. The term “oil field chemical” includes tracersand well treatment agents.

The term “tracer” means one or more compounds that can be used to tracethe movement of a material in a hydrocarbon reservoir, or to detect thecomposition or to measure the properties of specified areas of ahydrocarbon reservoir. The term “radioactive tracer” means a tracerwhich is radioactive. The term “chemical tracer” means a non-radioactivechemical compound that is used as a tracer.

The term “well treatment agent” refers to any of the various compoundsor mixtures placed within a well or hydrocarbon reservoir to address orprevent various undesired effects caused by a variety of conditionsincluding, but not limited to scale formation, salt formation, paraffindeposition, emulsification (both water-in-oil and oil-in-water), gashydrate formation, corrosion, asphaltene precipitation, and paraffinformation. Well treatment agents include, but are not limited to, scaleinhibitors, hydrate and halite inhibitors, corrosion inhibitors,biocides, wax and asphaltene control substances, demulsifiers, gelbreakers, drag reducers, salt inhibitors, gas hydrate inhibitors, oxygenscavengers, foaming agents, surfactants and well clean up substances(such as enzymes; organic molecules, acids, esters, and aliphaticcompounds).

The term “microcapsule” refers to a structure having an oil fieldchemical contained within the microcapsule by a microencapsulant. Amicrocapsule has either (a) a core comprising an oil field chemical witha shell around the core or (b) a micro-matrix comprising an oil fieldchemical with or without a shell.

The term “core” refers to the central inner portion of a composition.The core can be a simple phase of oil field chemicals, or a mixturecomprising one or more oil field chemicals and non-polymeric materials.The core can contain a mixture of a plurality of sub-cores andnon-polymeric materials. This configuration of a plurality of sub-coresis referred to as a “multicore.” Each of the sub-cores comprise one ormore oil field chemicals. Each of the sub-cores can be surrounded by apolymeric shell.

The term “matrix” refers to a three dimensional structure made ofpolymers.

The term “micro-matrix” refers to a three dimensional structure onmicro-scale, i.e., with a size from nanometer to sub-millimeter. Thethree dimensional structure is made of polymers and contains one or moreoil field chemicals distributed within the structure. A micro-matrix canbe regarded as a special type of core. It differs from normal cores inthat it has a 3-dimensional polymeric structure. The polymers can bepre-formed or formed in-situ by polymerization of monomers. Themicro-matrix can have oil field chemicals molecularly distributed in theentire micro-matrix structure or comprise a plurality of sub-cores, eachcontaining an oil field chemical.

“Microencapsulant” refers to all materials, either polymeric ornon-polymeric, within a microcapsule excluding oil field chemicalswithin the microcapsule and excluding non-polymeric materials withincores or multi-cores. Microencapsulants form a three-dimensionalstructure in the form of shells or micro-matrixes that contain thecores, sub-cores, multi-cores or oil field chemicals that aremolecularly dispersed in the microencapsulant.

The term “shell” refers to a polymeric coating that at least partiallysurrounds a core, a micro-matrix or an adjacent shell between the shelland a core or micro-matrix.

The term “bulk polymer” refers to one or more polymers that can becombined with a plurality of microcapsules, where each of themicrocapsules contains one or more oil field chemicals. Bulk polymerscan be combined with compositions containing microcapsules and havingvarious configurations described herein to obtain an article in the formof a final product, such as in the form of a film, strip, bead, two-partresin system, etc.

The term “embedding prepolymers and/or monomers” refers to prepolymersand/or monomers that are mixed with microcapsules and then reacted toform a bulk polymer in which microcapsules become mixed with, orembedded in the bulk polymer.

The term “derivative of” a compound, such as cellulose or starch, meansone or more compounds having the basic backbone of the compound, whereone of more groups in the compound has been reacted with one or morereactants and the basic structure remains. A derivative of a cellulosewould be a polysaccharide consisting of linear chains of large numbersof β-linked D-glucose units, where one or more of the hydroxyl groups isreacted with one or more compounds and the basic cellulose structureremains. A derivative of a starch would have a large number of glucoseunits joined by glycosidic bonds, where one or more of the groups withinthe starch have been chemically reacted with one or more reactants andthe basic starch structure remains.

The term “additive” refers to any compound or mixture that is introducedinto a bulk polymer to help incorporate the microcapsules and help formcompositions and articles.

The term “initiator” refers to one or more compounds that react with amonomer to form an intermediate compound capable of linking successivelywith a large number of other monomers into a polymeric compound.

The term “catalyst” refers to one or more compounds that catalyse thereaction of monomers and/or an intermediate compound to form a polymer.

The term “nanoparticle” refers to particles having at least onedimension (d) of ≤500 nm.

“Wt %” refers to the weight of a component or ingredient relative to thetotal dry weight of a composition, i.e., weight percent. For example, adosage form comprising 40 wt % of compound (1) that weighs 1000 mgcontains 400 mg of compound (1).

The term “cumulative % of the applied tracer (or oil field chemical)released” refers to the total percentage of the initial amount of atracer (or oil field chemical) that was released from a composition overa specific period of time under specific test conditions.

Oil Field Chemicals

In each of the compositions described herein, at least one oil fieldchemical is present within the core or micromatrix of the microcapsules.The oil field chemical is a tracer or well treatment agent. Preferably,the oil field chemical is a tracer, a corrosion inhibitor or a biocide.More than one oil field chemical can be incorporated into the core ormicro-matrix of the composition. When one or more oil field chemicalsare incorporated into the core or micro-matrix of the composition, theone or more oil field chemicals can be mixed together or can be presentin the core or micro-matrix in discrete structures, such as in amulti-core structure. When the core or micro-matrix contains two or moreoil field chemicals, all of the oil field chemicals can be oil solubleor water soluble, or the compounds can be a mixture of water soluble andoil soluble compounds. When the core or micro-matrix contains two ormore oil field chemicals, one or more of the compounds can partitionbetween oil and water, or can partition between a fluid and gas in thereservoir. One or more oil field chemicals can also be present in one ormore shells surrounding the core. When two or more oil field chemicalsare present in the composition, all of the oil field chemicals can beoil soluble oil field chemicals, all of the oil field chemicals can bewater soluble oil field chemicals, or the oil field chemicals can be amixture of oil soluble oil field chemicals and water soluble oil fieldchemicals. When two or more oil field chemicals are present in thecomposition, at least one of the oil field chemicals is located within acore or micro-matrix.

The oil field chemicals are not chemically linked or bound to, and donot react with, any other components of the composition.

The oil field chemicals can be solids, liquids or gases at thetemperature at which the chemicals are to be released. One of theadvantages of the use of the compositions and articles described herein,is that gaseous, liquid and/or solid oil field chemicals can beincorporated into the compositions or articles described herein, andthen delivered to the targeted hydrocarbon reservoir or well, where theyare slowly released into fluids (liquid or gas) in the reservoir orwell.

Solid oil field chemicals can be pre-treated to have a desired range ordistribution of particle sizes by milling or grinding. Oil fieldchemicals can be used alone or mixed with non-polymeric compounds. Theoil field chemicals, either alone or as mixtures, can form cores,sub-cores or multicores in a microcapsule. Oil field chemicals can alsoexist in the form of molecules individually distributed in amicro-matrix or shell in a microcapsule. Non-polymeric compounds thatcan be mixed with oil field chemicals include, but are not limited to,solvents or waxes. Examples of solvents are toluene, xylene,cyclohexane, castor oil, etc. Examples of waxes are cetyl palmitate andcaster wax.

Tracers

Any chemical compound can be used as a tracer within the presentinvention if it can be detected within one or more fluids within areservoir and does not interfere or interact undesirably with othermaterials present in the oil well at the levels used. Preferably, beforethe tracer is added to the well, the tracer is not present at ameasurable level in reservoir fluids from the well to be tested. Thismeans that background levels of the tracer should be less than the limitof detection. It is also preferred that the tracer can be measured atlevels sufficiently low to allow its use to be economical. While upperlimits for the concentration of the tracer in reservoir fluid can be ashigh as about 10,000 parts per million, for a variety of reasons, suchas economical, toxicological, causing unacceptable interactions withother materials present in an oil well, etc. the tracers can bedetectable at a range of from about 1 part per quadrillion to about 500parts per million in the fluid being analyzed. Preferably the tracersare detectable at a range of from 1 part per trillion to about 50 partsper million. More preferably the tracers are detectable at a range offrom 5 parts per trillion to about 10 parts per million. Preferably thetracer is not a radioactive tracer.

Tracers can be solids, liquids or gases at room temperature and can bereleased to either a liquid or a gas inside a hydrocarbon reservoir.

The tracers can be present in the compositions in an amount from about0.5% to about 80% by weight of the total composition, preferably fromabout 2% to about 65% by weight of the total composition, morepreferably from about 5% to about 50% by weight of the totalcomposition. The amount of tracer present in the compositions can bebased upon the elution profile and the expected concentration in thereservoir fluid into which the tracer will move when eluted from thecompositions. Concentrations of the tracer in the eluent can be at leastabout 1 part per quadrillion and preferably at a concentration of lessthan or equal to 10,000 parts per million. Preferably the concentrationof the tracer in the eluent is from about 100 parts per trillion toabout 100 parts per million.

Oil Soluble Tracers

Tracers used to track the movement of oil soluble materials generallyhave low water solubility and high (>1000) organic/water partitioncoefficients. Several families of such compounds have been used.Illustrative examples of suitable tracer compounds of the presentinvention are organic compounds selected from the hydrocarbons andhalogenated hydrocarbons. Mixtures of these compounds can also be usedalthough single compounds are preferred. The tracer compound canpreferably be a halogenated aromatic, polycyclic aromatic, heterocyclicaromatic, aromatic ketone, cycloalkane, or aliphatic compound, where thecompound including at least one halogen selected from the groupconsisting of Br, Cl, F and I. Suitable tracers include, but are notlimited to 4-iodotoluene, 1,4-dibromobenzene, 1-chloro-4-iodobenzene,5-iodo-m-xylene, 4-iodo-o-xylene, 3,5-dibromotoluene, 1,4-diiodobenzene,1,2-diiodobenzene, 2,4-dibromomesitylene, 2,4,6-tribromotoluene,1-iodonaphthalene, 2-iodobiphenyl, 9-bromophenanthrene,2-bromonaphthalene, bromocyclohexane, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1-bromododecane, bromooctane,1-bromo-4-chlorobenzene, bromobenzene, 1,2,3-trichlorobenzene,4-chlorobenzylchloride, 1-bromo-4-fluorobenzene,perfluoromethylcyclopentane (PMCP), perfluoromethylcyclohexane (PMCH),perfluorodimethylcyclobutane (PDMCB), m-perfluorodimethylcyclohexane(m-PDMCH), o-perfluorodimethylcyclohexane (o-PDMCH),p-Perfluorodimethylcyclohexane (p-PDMCH), perfluorotrimethylcyclohexane(PTMCH), perfluoroethylcyclohexane (PECH), andperfluoroisopropylcyclohexane (IPPCH).

Oil soluble tracers can also be oil dispersible nanoparticles which maybe detected by analytical techniques such as light absorption andemission (e.g., Raman, UV, IR and fluorescence) or electrochemicalmethods.

Water Soluble Tracers

Water soluble tracers can be used to trace the movement of productionfluids containing water. Groups of compounds that are commonly describedin the art as dyes, pigments, and colorants can be used. These compoundsare often visible to the eye in either ambient or ultraviolet light.Suitable tracers useful with the present invention include but are notlimited to those selected from the group consisting of: Acridine Orange;2-anthracenesulfonic acid, sodium salt; Anthrasol Green IBA (SolubilizedVat Dye); bathophenanthrolinedisulfonic acid disodium salt; amino2,5-benzene disulfonic acid; 2-(4-aminophenyl)-6-methylbenzothiazole;Brilliant Acid Yellow 8G (Lissamine Yellow FF, Acid Yellow 7); CelestineBlue; cresyl violet acetate; dibenzofuransulfonic acid, 1-isomer;dibenzofuransulfonic acid, 2-isomer; 1-ethylquinaldinium iodide;fluorescein; fluorescein, sodium salt (Acid Yellow 73, Uranine);Keyfluor White ST (Flu. Bright. 28); Keyfluor White CN; Leucophor BSB(Leucophor AP, Flu. Bright. 230); Leucophor BMB (Leucophor U, Flu.Bright. 290); Lucigenin (bis-N-methylacridinium nitrate); mono-, di-, ortri-sulfonated naphthalenes, including but not limitedto—1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (1,5-NDSAhydrate); 2-amino-1-naphthalenesulfonic acid;5-amino-2-naphthalenesulfonic acid;4-amino-3-hydroxy-1-naphthalenesulfonic acid;6-amino-4-hydroxy-2-naphthalenesulfonic acid;7-amino-1,3-naphthalenedisulfonic acid, potassium salt;4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid;5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalenesulfonic acid; 1-amino-7-naphthalene sulfonic acid; and2,6-naphthalenedicarboxylic acid, dipotassium salt;3,4,9,10-perylenetetracarboxylic acid; Phorwite CL (Flu. Bright. 191);Phorwite BKL (Flu. Bright. 200); Phorwite BHC 766; Pylaklor White S-15A;1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt; pyranine,(8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt); quinoline;Rhodalux; Rhodamine WT; Safranine O; Sandoz CW (Flu. Bright, 235);Sandoz CD (Flu. Bright. 220); Sandoz TH-40; Sulforhodamine B (Acid Red52); Tinopal 5BM-GX; Tinopol DCS; Tinopal CBS-X; Tinopal RBS 200; TitanYellow (Thiazole Yellow G), and any existing ammonium, potassium andsodium salts thereof. Preferred fluorescent tracers are1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt and1,5-naphthalenedisulfonic acid, disodium salt (hydrate).

Water soluble tracers can also be water dispersible nanoparticles, whichmay be detected by analytical techniques such as light absorption andemission (e.g., Raman, UV, IR and fluorescence) and electrochemicalmethods.

Preferably the chemical tracers useful with the present inventioninclude, but are not limited to: halogenated benzoic acids, salts andcompounds derived from the acid such that they hydrolyze to form theacids, or salts thereof, in the reservoir, including 2-fluorobenzoicacid; 3-fluorobenzoic acid; 4-fluorobenzoic acid; 3,5-difluorobenzoicacid; 3,4-difluorobenzoic acid; 2,6-difluorobenzoic acid;2,5-difluorobenzoic acid; 2,3-difluorobenzoic acid; 2,4-difluorobenzoicacid; pentafluorobenzoic acid; 2,3,4,5-tetrafluorobenzoic acid;4-(trifluoro-methyl)benzoic acid; 2-(trifluoromethyl)benzoic acid;3-(trifluoro-methyl)benzoic acid; 3,4,5-trifluorobenzoic acid;2,4,5-trifluorobenzoic acid; 2,3,4-trifluorobenzoic acid;2,3,5-trifluorobenzoic acid; 2,3,6-trifluorobenzoic acid;2,4,6-trifluorobenzoic acid and the brominated, chlorinated andiodinated analogs thereof. When more than one halogen atom is present onthe benzoic acid, the halogens can be the same or different. Preferably,the salts of the halogenated benzoic acids are sodium salts or potassiumsalts.

Well Treating Agents

Numerous types of well treating agents are known in the art. Welltreating agents are used to inhibit, control, prevent or treat variousconditions that can affect the reservoir and the production of oiland/or gas from the reservoir. Well treating agents are generallydescribed in families based on the function they perform, such as scaleinhibitors, asphaltene dispersants and inhibitors, acid stimulationchemicals, sand control agents, napthenate and other carboxylateanti-fouling agents, corrosion control agents, gas hydrate controlagents, wax (paraffin wax) control agents, demulsifiers, foam controlagents, flocculants, biocides, hydrogen sulfide scavengers, oxygenscavengers, drag-reducing agents (DRA's), hydrotesting chemicals andfoamers for gas well deliquification. In many cases, it would be helpfulif well treating agents were able to be slowly released over time tohelp maintain the well treating agent at an effective concentration inthe well or reservoir. Various types of well treating agents aredescribed by Malcolm A. Kelland in Production Chemicals for the Oil andGas Industry, Second Edition Hardcover, 16 Apr. 2014.

Biocides include oxidising biocides; nonoxidizing organic biocides, suchas aldehydes, quaternary phosphonium compounds, quaternary ammoniumcompounds, cationic polymers, organic bromides, metronidazole,isothiazolones (or isothiazolinones) and thiones, organic thiocyanates,phenolics, alkylamines, diamines and triamines, dithiocarbamates,2-decylthiolethanamine and hydrochloride salts, triazine derivatives,and oxazolidines; and biostats (control “biocides” or metabolicinhibitors), such as anthraquinone, nitrates and nitrites. Specificexamples of biocides include acrolein, bronopol,2,2-dibromo-3-nitrilopropionamide, formaldehyde, glutaraldehyde,tetrakishydroxymethyl phosphonium sulfate (THPS), [NR₁R₂R₃R₄]⁺Cl⁻ (whereR₁=alkyl(C₁₄-C₁₈) and R₂, R₃, and R₄=methyl or benzyl or R₁ andR₂=alkyl(C₁₀) and R₃ and R₄=methyl), dibromonitrilopropioanamide(DBNPA), Dazomet (MITC), tributyl tetradecyl phosphonium chloride(TTPC), halogenated oxidizers, dithiocarbamate, methylene bisthiocyanate(MBT), didecylmethylquat, methylbenzylcocuat, cocodiamine diacetate,cocodiamine, and chlorine dioxide.

Scale inhibitors include polyphosphonates, phosphate esters,nonpolymeric phosphonates and aminophosphonates, polyphosphonates,phosphino polymers and polyphosphinates, polycarboxylates, biodegradablepolycarboxylates and polysulfonates. Exemplary anionic scale inhibitorsinclude strong acidic materials such as a phosphonic acid, a phosphoricacid or a phosphorous acid, phosphate esters, phosphonate/phosphonicacids, the various aminopoly carboxylic acids, chelating agents, andpolymeric inhibitors and salts thereof. Included are organophosphonates, organo phosphates and phosphate esters as well as thecorresponding acids and salts thereof. Phosphonate/phosphonic acid typescale inhibitors are often preferred in light of their effectiveness tocontrol scales at relatively low concentration. Polymeric scaleinhibitors, such as polyacrylamides, salts of acrylamido-methyl propanesulfonate/acrylic acid copolymer (AMPS/AA), phosphinated maleiccopolymer (PHOS/MA) or sodium salt of polymaleic acid/acrylicacid/acrylamido-methyl propane sulfonate terpolymers (PMA/AMPS), arealso effective scale inhibitors. Sodium salts are preferred.

Asphaltene dispersants and inhibitors include low molecular weight,nonpolymeric asphaltene dispersants, such as low-polarity nonpolymericaromatic amphiphiles, sulfonic acid-base nonpolymeric surfactantasphaltene dispersants, nonpolymeric surfactant asphaltene dispersantswith acidic head groups, amide and imide nonpolymeric surfactantasphaltene dispersants, and alkylphenols and related asphaltenedispersants; and oligomeric (resinous) and polymeric asphaltenedispersants, such as alkylphenol-aldehyde resin oligomers, polyester andpolyamide/imide asphaltene dispersants and asphaltene dissolvers.Exemplary asphaltene treating chemicals include, but are not limited to,fatty ester homopolymers and copolymers (such as fatty esters of acrylicand methacrylic acid polymers and copolymers) and sorbitan monooleate.

Acid stimulation chemicals include corrosion inhibitors for acidizing,nitrogen based corrosion inhibitors, oxygen-containing corrosioninhibitors, including those with unsaturated linkages, corrosioninhibitors containing sulphur, ion control agents, water wetting agents,oil-wetting agents, weak organic acids, weak sandstone-acidizingfluorinated agents, buffered acids, gelled or viscous acids, foamedacids, temperature-sensitive acid-generating chemicals and enzymes andemulsified acids.

Sand control agents include resins and organosilanes.

Anti-fouling agents include napthenate and other carboxylateanti-fouling agents.

Corrosion control agents include film-forming corrosion inhibitors(FFCI's) such as phosphate esters, amine salts of polycarboxylic acids,quaternary ammonium and iminium salts and zwitterionics, amidoimines andimidazolines, amides, polyhydroxy and ethoxylated amines/amides,nitrogen containing heterocycles, sulfur containing compounds andpolyamino acids. Exemplary corrosion inhibitors include, but are notlimited to, fatty imidazolines, alkyl pyridines, alkyl pyridinequaternaries, fatty amine quaternaries and phosphate salts of fattyimidazolines.

Gas hydrate control agents include thermodynamic hydrate inhibitors(THI's); kinetic hydrate inhibitors (KHI's), such as vinyl lactam KHIpolymers, hyperbranched polyester amide KHI's, pyroglutamate KHIpolymers and polydialkylmethacrylamide KHI's; anti-agglomerates (AA's),such as emulsion pipeline AA's, hydrate-philic pipeline AA's, naturalsurfactants and nonplugging oils, gas well AA's and gas hydrate plugremoval agents. Exemplary gas hydrate control agents include, but arenot limited to, polymers and homopolymers and copolymers of vinylpyrrolidone, vinyl caprolactam and amine based hydrate inhibitors suchas those disclosed in U.S. Patent Publication Nos. 2006/0223713 and2009/0325823, both of which are herein incorporated by reference.

Wax (paraffin wax) control agents include wax solvents, thermochemicalwax control packages, chemical wax prevention agents, such as waxinhibitors, ethylene polymers and copolymers, comb polymers (methacrylicester polymers and maleic copolymers), wax dispersants and polar crudefraction flow improvers. Exemplary paraffin inhibitors useful for thepractice of the present invention include, but are not limited to,ethylene/vinyl acetate copolymers, acrylates (such as polyacrylateesters and methacrylate esters of fatty alcohols), and olefin/maleicesters.

Demulsifiers include polyalkoxylate block copolymers and esterderivatives, alkylphenol-aldehyde resin alkoxylates, polyalkoxylates ofpolyols or glycidyl ethers, polyamine polyalkoxylates and relatedcationic polymers, polyurethanes (carbamates) and polyalkoxylatederivatives, hyperbranched polymers, vinyl polymers, polysilicones,dual-purpose demulsifiers and biodegradable demulsifiers. Exemplarydemulsifying agents include, but are not limited to, condensationpolymers of alkylene oxides and glycols, such as ethylene oxide andpropylene oxide condensation polymers of di-propylene glycol as well astrimethylol propane; and alkyl substituted phenol formaldehyde resins,bis-phenyl diepoxides, and esters and diesters of such di-functionalproducts. Preferred non-ionic demulsifiers are oxyalkylated phenolformaldehyde resins, oxyalkylated amines and polyamines, di-epoxidizedoxyalkylated polyethers, etc. Suitable oil-in-water demulsifiers includepoly triethanolamine methyl chloride quaternary, melamine acid colloid,aminomethylated polyacrylamide, etc.

Foam control agents include defoamers and antifoamers, such as siliconesand fluorosilicones, and polyglycols. Exemplary foaming agents include,but are not limited to, oxyalkylated sulfates or ethoxylated alcoholsulfates, or mixtures thereof.

Flocculants include cationic polymers such as dialkyldimethylammoniumchloride polymers, acrylamide or acrylate-based cationic polymers;environmentally-friendly cationic polymeric flocculants;dithiocarbamates; anionic polymers and amphoteric polymers.

Hydrogen sulfide scavengers include nonregenerative H₂S scavengers, suchas solid scavengers, oxidising chemicals, aldehydes, reaction productsof aldehydes and amines, such as triazines, and metal carboxylates andchelates.

Oxygen scavengers include dithionite salts, hydrazine and guanidinesalts, hydroxylamines and oximes, activated aldehydes and polyhydroxylcompounds, catalytic hydrogenation agents, enzymes, sulfided ironreagents, bisulfite, metabisulfite and sulphate salts. Exemplary oxygenscavengers include triazines, maleimides, formaldehydes, amines,carboxamides, alkylcarboxyl-azo compounds, cumine-peroxide compounds,morpholino and amino derivatives, morpholine and piperazine derivatives,amine oxides, alkanolamines, aliphatic and aromatic polyamines.

Drag-reducing agents (DRA's) include oil-soluble DRA's, such aspolyalkene (polyolefin) DRA's and polymethacrylate ester DRA's, andwater-soluble DRA's, such as polysaccharides and derivatives,polyethylene oxide DRA's, acrylamide-based DRA's and water-solublesurfactant DRA's. Exemplary surfactants include cationic, amphoteric,anionic and nonionic surfactants. Cationic surfactants include thosecontaining a quaternary ammonium moiety (such as a linear quaternaryamine, a benzyl quaternary amine or a quaternary ammonium halide), aquaternary sulfonium moiety or a quaternary phosphonium moiety ormixtures thereof. Suitable surfactants containing a quaternary groupinclude quaternary ammonium halide or quaternary amine, such asquaternary ammonium chloride or a quaternary ammonium bromide.Amphoteric surfactants include glycinates, amphoacetates, propionates,betaines and mixtures thereof. The cationic or amphoteric surfactant canhave a hydrophobic tail (which can be saturated or unsaturated) such asa C₁₂-C₁₈ carbon chain length. Further, the hydrophobic tail can beobtained from natural oil from plants such as one or more of coconutoil, rapeseed oil and palm oil. Preferred surfactants includeN,N,N-trimethyl-1-octadecammonium chloride:N,N,N-trimethyl-1-hexadecammonium chloride; andN,N,N-trimethyl-1-soyaammonium chloride, and mixtures thereof. Suitableanionic surfactants are sulfonates (like sodium xylene sulfonate andsodium naphthalene sulfonate), phosphonates, ethoxysulfates and mixturesthereof.

Hydrotesting chemicals include biocides, oxygen scavengers, corrosioninhibitors, dyes and environmentally friendly agents.

Foamers for gas well deliquification can also be used.

Microencapsulant

The microencapsulant can comprise any known polymer material that canform the major portion of a shell or micro-matrix to microencapsulate anoil field chemical. Examples of such materials include, but are notlimited to melamine-formaldehyde, urea-formaldehyde, phenol-formaldehyderesin, melamine-phenol-formaldehyde resin, furan-formaldehyde resin,epoxy resin, ethylene-vinyl acetate copolymer,polypropylene-polyethylene copolymer, polyacrylates, polyesters,polyurethane, polyamides, polyethers, polyimides, polyether etherketones, polyolefins, polystyrene and functionalized polystyrene,polyvinylalcohol, polyvinylpyrrolidone, cellulose and cellulosederivatives, starch and starch derivatives, polysiloxanes, and mixturesthereof.

The materials used to form the shell or micro-matrix can also includenon-organic-materials, such as silica, calcium carbonate or inorganicpolymers, such as polyphosphazenes. The materials used to form the shellor micro-matrix can be organic/inorganic hybrid materials, such ashybrid silica/polyamide materials.

In addition to shell or micro-matrix forming polymers and inorganicmaterials, microencapsulants can further comprise emulsifiers and/orstabilisers.

An emulsifier is a surfactant which when present in small amountsfacilitates the formation of an emulsion, or enhances its colloidalstability by decreasing either or both of the rates of aggregation andcoalescence. [IUPAC. Compendium of Chemical Terminology, 2nd ed. (the“Gold Book”). Compiled by A. D. McNaught and A. Wilkinson. BlackwellScientific Publications, Oxford (1997). XML on-line corrected version:http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B.Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.doi:10.1351/goldbook.] Emulsifiers can be cationic, anionic andnon-ionic. They can be either low molecular weight or polymeric. Examplesurfactants include mono- and diglycerides of acetic acid, citric acid,lactic acid, fatty acids, monoglycerides, lecithins, sorbitan fatty acidesters, polyoxyethylene sorbitan esters, sodium lauryl sulphate, sodiumlaureth sulphate, sodium dodecylbenzesulfonate, dodecyl trimethylammonium bromide, hexydecyl trimethyl ammonium bromide, etc.

Stabilizers are substances that are added to a system, such as anemulsion, to prevent or retard a change in the system. Some compoundscan function as both emulsifiers and stabilizers, and many stabilizersare polymeric. Examples of stabilizers are: homo- and copolymers ofpolyvinylalcohol, polyvinylpyrrolidone, polyacrylic acid, sodiumcarboxyl methylcellulose, hydroxylmethylcellulose,hydroxylpropylcellulose, starch derivatives, maleic-anhydride copolymerssuch as ethylene-maleic-anhydride copolymer, styrene-maleic anhydridecopolymers, vinyl acetate-maleic anhydride copolymer, vinyl ether-maleicanhydride copolymer, methyl vinyl ether-maleic anhydride copolymer,octadecyl vinyl ether-maleic anhydride copolymer, anethylene-vinylacetate copolymer, a polyacrylic acid based copolymer, apolyvinylpyrrolidone based copolymer, a polyacrylate based copolymer, apolyacrylamide, a polyacrylamide based copolymer, and mixtures thereof.Stabilizers known as Pickering stabilisers that comprise organic orinorganic nano or micro particles, can also be used.

Preferably, the polymeric microencapsulant is a melamine-formaldehyde, aurea-formaldehyde, a phenol-formaldehyde resin, amelamine-phenol-formaldehyde resin, a furan-formaldehyde resin, an epoxyresin, a polysiloxane, a polyacrylate, a polyester, a polyurethane, apolyamide, a polyether, a polyimide, a polyolefin,polypropylene-polyethylene copolymers, polystyrene, functionalizedpolystyrene derivatives, gelatin, a gelatin derivative, cellulose, acellulose derivative, starch or a starch derivative, a polyvinylalcohol, an ethylene-vinylacetate copolymer, anethylene-maleic-anhydride copolymer, a styrene-maleic anhydridecopolymer, a vinyl acetate-maleic anhydride copolymer, a vinylether-maleic anhydride copolymer, a methyl vinyl ether-maleic anhydridecopolymer, an octadecyl vinyl ether-maleic anhydride copolymer, apolyacrylamide, a polyacrylic acid, a polyvinylpyrrolidone, apolyvinylpyrrolidone based copolymer, a polyacrylate based copolymer, apolyacrylamide, a polyacrylamide based copolymer, and mixtures thereof.More preferably, the microencapsulant comprises a vinyl ester, an epoxyresin, polyurethane, a crosslinked polystyrene copolymer, a crosslinkedpolyacrylate, a melamine-formaldehyde resin, a urea-formaldehyde resinor a phenol-formaldehyde resin.

Bulk Polymer

Bulk polymer refers to one or more polymers that can be combined with aplurality of microcapsules, each containing one or more oil fieldchemicals, or can be combined with compositions containing microcapsulesto obtain a final product in the form of a solid having a shape such asa film, a strip, a bead, etc.

Bulk polymers can be any solid or solid-forming polymer, preferably athermosetting polymer, a thermoplastic polymer, or a blend thereof. Theblends can be a blend of thermosetting polymer with one or morethermosetting polymers, a blend of thermoplastic polymer with one ormore thermoplastic polymers, or a blend of one or more thermoplasticpolymers with one or more thermosetting polymers. The thermosettingpolymers can be an epoxy resin, polyester, polyurethane, an acrylicpolymer, a phenol-formaldehyde resin, a melamine-formaldehyde resin or afuran-formaldehyde resin, etc. The thermoplastic polymers can be apolypropylene (isotactic or syndiotactic), a polyethylene, athermoplastic polyurethane, a polyether, a polyester (such aspolyethyleneterephthalate, polybutyleneterephthalate), apolyvinyldifluoroethylene, a polyamide, an acrylic polymer, a polyimide,a polyether ether ketone, cellulose, a cellulose derivative, or astarch, and mixtures thereof. Preferably, the bulk polymer comprises apolyethylene, a polypropylene, a polyacrylate, an aliphatic polyamide(such as nylon-6, nylon-12), a polyurethane, a vinyl ester, an epoxyresin or a polybutylene terephthalate.

Existing commercial polymers can be used as bulk polymers. Bulk polymercan also be formed by polymerization and or crosslinking of monomers,oligomers or prepolymers through processes described below.

Additives

Additives can be used in combination with bulk polymers to incorporatemicrocapsules and form compositions and articles. Additives includeadhesive agents and property improving agents.

Adhesive agents can be any material compatible with the bulk polymerinto which the microcapsules can be incorporated that provide additionalor improved adhesion between two different materials. Examples includeinorganic additives, such as fumed silica and precipitated calciumcarbonate, and copolymers such as ethylene-methacrylate copolymers,ethylene-maleic anhydride copolymers, oxidised polyethylene, oxidisedpolypropylene, acrylate-styrene copolymer, ethylene-acrylate copolymer,propylene-acrylate copolymer, propylene-methacrylate copolymers,propylene-ethylene oxide copolymers, and acrylonitrile-butadiene-styrenecopolymers.

Property improving agents are additives added to bulk polymers toimprove the properties such as mechanical strength, anti-abrasion,thermal stability of the final compositions and articles. Additivesacting as property improving agents include, but are not limited tofillers/extenders, toughening agents, plasticisers, antistatic agents,light stabilisers, heat stabilizers, antioxidants,antimicrobials/biostabilizers, blowing agents, flame retardants,pigments, impact modifiers, lubricants, process aids and reinforcingagents.

One type of preferred additives are inorganic nanoparticles such asfumed silica, aluminium oxide nanoparticles, nano clay such asnano-bentonite, and precipitated calcium carbonate. Other types ofpreferred additives are carbon nanotubes and carbon fibers. The additivecan be selected from the group consisting of a precipitated carbonate, acarbon nanotube, a fumed silica, carbon fiber, or polymericcompatibilizer selected from the group consisting of anethylene-acrylate copolymer, an ethylene-methacrylate copolymer,ethylene-maleic anhydride copolymers, a propylene-acrylate copolymer,propylene-methacrylate copolymers, oxidised polypropylene, oxidisedpolyethylene, oxidised propylene-ethylene copolymers, styrene-acrylatecopolymers and acrylonitrile-butadiene-styrene copolymers.

Compositions

The compositions and articles described herein are based on a mixture ofa bulk polymer with microcapsules encapsulating at least one oil fieldchemical. A composition comprises: (a) microcapsules comprising an oilfield chemical and a microencapsulant, where the microcapsules have anouter surface, and the oil field chemical is contained within themicrocapsules and (b) a bulk polymer, where the microcapsules areembedded within the bulk polymer. The microcapsules can comprise: (a) acore comprising an oil field chemical and a first shell comprising amicroencapsulant located adjacent to the core, or (b) a matrixcomprising an oil field chemical entrapped within a micro-matrixcomprising a microencapsulant.

Microcapsules

The microcapsules can comprise at least one of the following structures:

-   (a) a core shell structure comprising (i) a core comprising at least    one oil field chemical and (ii) a shell comprising a polymeric    microencapsulant;-   (b) a core multi-shell structure comprising (i) a core comprising at    least one oil field chemical, (ii) a first shell comprising a    polymeric microencapsulant located adjacent to the core; and (iii)    one or more additional shells located over the first shell, each    additional shell comprising a polymeric microencapsulant that is    different than the polymeric microencapsulant in an adjacent shell;-   (c) a multi-core shell structure comprising (i) a core comprising a    plurality of sub-cores where each sub-core comprises at least one    oil field chemical, and optionally having a shell at least partially    covering each of the sub-cores, and the sub-cores are dispersed in a    non-polymeric compound, and (ii) a shell comprising a polymeric    microencapsulant;-   (d) a micro-matrix structure comprising a core comprising at least    one oil field chemical entrapped within a micro-matrix comprising a    polymeric microencapsulant;-   (e) a micro-matrix with a shell structure comprising (i) a core    comprising at least one oil field chemical entrapped within a    micro-matrix comprising a polymeric microencapsulant; and (ii) a    shell comprising a polymeric microencapsulant;-   (f) a multi-core-micro-matrix with a shell structure comprising (i)    a micro-matrix comprising a plurality of sub-cores, where each    sub-core comprises at least one oil field chemical, and the    sub-cores are entrapped within the micro-matrix, and (ii) a shell    comprising a polymeric microencapsulant.

FIG. 1A depicts a core shell structure (1) comprising (i) a core (2)comprising at least one oil field chemical and (ii) a shell (3)comprising a polymeric microencapsulant.

FIG. 1B depicts a core multi-shell structure (10) comprising (i) a core(2) comprising at least one oil field chemical, (ii) a first shell (3)comprising a polymeric microencapsulant; and (iii) one or moreadditional shells (4) that at least partially cover the first shell.

FIG. 1C depicts a multi-core shell structure (11) comprising (i) a core(12) comprising a plurality of sub-cores (1) each comprising at leastone oil field chemical within the sub-core (2) and optionally having ashell (5) at least partially covering the sub-cores, and (ii) a shell(3) comprising a polymeric microencapsulant around the core. Themulti-core shell structure can also contain one or more additionalshells that at least partially cover the first shell as shown in FIG. 1Bas item (4).

FIG. 1D depicts a micro-matrix (13) comprising at least one oil fieldchemical entrapped within a three-dimensional polymeric microencapsulant(7).

FIG. 1E depicts a micro-matrix with a shell structure (14) comprising(i) a micro-matrix (7) comprising at least one oil field chemicalentrapped within the micro-matrix, (ii) a first shell (3) comprising apolymeric microencapsulant, where the first shell at least partiallycovers the micro-matrix; and (iii) one or more additional shells (4)that at least partially cover the first shell. The structure can haveonly a first shell (3) and not have one or more additional shells (4).

FIG. 1F depicts a multi-core-micro-matrix with a shell structure (15)comprising (i) a core (12) comprising a micro-matrix (7) comprising athree-dimensional polymeric microencapsulant and a plurality of subcores(9) within the micro-matrix, (ii) a first shell (3) comprising adifferent polymeric microencapsulant. The structure can also contain oneor more additional shells (not shown) that at least partially cover thefirst shell, as shown as item 4 in FIG. 1E.

The microcapsules, cores and shells are shown graphically in FIGS. 1A-1Fas circles for ease of illustration. The microcapsules can have anyshape, including, but not limited to a sphere, a rod, an ovoid, apseudo-cuboid, a ring, etc.

The microcapsules comprise two groups of components: oil field chemicalsand microencapsulants. Microencapsulants comprise organic polymer and/orinorganic materials. The microencapsulant can further compriseemulsifiers, stabilisers or both. The microencapsulant can form shellsand/or a micro-matrix in a microcapsule. The oil field chemicals arecontained by the microencapsulants. The oil field chemical can bepresent at 1 to 99.5% by weight of the microcapsule. Preferably the oilfield chemical is present at 10 to 98% by weight of the microcapsule. Inone aspect of the invention, the oil field chemicals or their mixtureswith non-polymeric compounds form cores, sub-cores or multi-cores. Theoil field chemicals can be present at 2 to 100% by weight of the totalcore or micro-matrix in a microcapsule. Preferably the oil fieldchemicals are present at 5 to 100% by weight of total weight of thecores.

In another aspect of the invention, individual molecules of oil fieldchemicals can be distributed in micro-matrixes or shells. Thecomposition can comprise microcapsules comprising a core that is asimple core or a multi-core, or a micro-matrix. The composition cancomprise microcapsules comprising two or more shells, where each shellcomprises a polymeric microencapsulant that is different than thepolymeric microencapsulant in an adjacent shell. The composition cancomprise microcapsules comprising two or more shells, where one or moreshells comprise an additive or an oil field chemical.

In one aspect of the invention, the microcapsules comprise one or moreshells. Microcapsules having core-multi-shell, micro-matrix-shell, ormicromatrix-multi-shell structures can have additional shells. Theseadditional shells can comprise a microencapsulant that is either thesame as, or different than, the microencapsulant in the first shell orthe micro-matrix. For microcapsules with one or more shells, the outersurface of the outer shell of the microcapsule is the outer surface ofthe microcapsule. In another aspect of the invention, the microcapsulescomprise micro-matrices without shells. For these microcapsules, theouter surface of the micro-matrices is the outer surface of themicrocapsules. The outer surface of the microcapsule is part of themicrocapsule. The composition can comprise microcapsules where the outersurface of the microcapsule is not reactive with the bulk polymer. Thecomposition can comprise microcapsules where the outer surface of themicrocapsule comprises one or more groups that are reactive with thebulk polymer.

One or more oil field chemicals are present within a microcapsule.Additional shells can be present in core-shell, multi-core-shell,core-multi-shell, micro-matrix-shell or micro-matrix-multi-shellstructures. These additional shells can comprise oil field chemicalsthat are either the same or different from the oil field chemicals inthe core, multicores, first shell or the micro-matrix. Preferably, theoil field chemicals in all the shells in a microcapsule can account for0-49.5% by weight of the total amount oil field chemicals in amicrocapsule. More preferably the oil field chemicals in all the shellsaccount for 0-30% by weight of the total oil field chemicals in amicrocapsule.

The microencapsulant can be present at 10-100% of the mass of theshells. Preferably, the microencapsulant is present at 20-100% of themass of the shells. The microencapsulant can be present at 0.2 to 95% byweight of the total composition. Within the microcapsules, the shellscan account for 0.5-95% by weight of the total weight of themicrocapsules and the cores account for 5-99.5%, by weight of the totalweight of the microcapsules.

The microcapsules can have a volume weighted average particle size ofbetween 0.05 μm and 600 μm, inclusive. Preferably the average particlesize is between 0.1 μm and 500 μm, inclusive. The size of themicrocapsules can be determined by a laser diffraction technique using aMalvern or Sympatec instrument. This method measures the volume weighteddiameter of sphere particles directly. For non-spherical particles,volume equivalent spherical diameter is measured. Mean (arithmeticaverage), mode (most frequent) or median (where 50% of the population isbelow/above) values may be taken as representative particle size of apopulation. As used herein, the measured volume weighted mean diameterof the microcapsules is taken as the representative particle size of themicrocapsules.

In one aspect of the invention, the microcapsules can comprisemicroencapsulants that provide one or more functional groups at theouter surface of the microcapsules that can react with the bulkpolymers. The functional groups can be carboxylates, amines, anhydrides,hydroxyls, isocyanates, phosphates, nitriles, esters, aldehydes,N-methylol, silanol etc.

In a further aspect of the invention, the microcapsules can comprisemicroencapsulants that provide one or more functional groups at theouter surface of the microcapsules that will allow for strong physicalinteraction (e.g. dipole-dipole interaction and hydrogen bonding etc.)between the surface of the microcapsules and the bulk polymers. Thefunctional groups may not react with the bulk polymers. The oilfieldchemicals do not chemically react with the microencapsulant or bulkpolymer.

In another aspect of the invention, a composition comprises (a)microcapsules, (b) a bulk polymer and (c) optionally one or moreadditives, where the microcapsules are embedded, preferablyhomogeneously, in the bulk polymer, where the microcapsules comprise acore and at least a shell, a micro-matrix, or a micromatrix with one ormore shells, where the core or micro-matrix comprise at least one oilfield chemical, and the shell at least partially covers the core ormicro-matrix. The bulk polymeric material can account for 20-98% byweight of the total weight of the composition. The microcapsules canaccount for 2-80% by weight of the total weight of the composition. Theone or more additives can account for 0-30% by weight of the totalweight of the composition. The composition can further comprise one ormore bulk polymers and/or one or more additives. Additives include (a)adhesive agents and (b) property improving agents. Additives can be usedin combination with bulk polymers to incorporate microcapsules into thebulk polymers and in forming compositions and articles. Propertyimproving agents can be distributed within the bulk polymers. Adhesiveagents can be present at the surface of the microcapsules and/or in thebulk polymeric material.

In one aspect of the invention, the composition can comprise one or moreoil field chemicals that are located outside the microcapsules and aredistributed in the bulk polymers. These oil field chemicals can be thesame or different than the oil field chemicals in the microcapsules. Oilfield chemicals outside the microcapsules that are located in the bulkpolymer can account for 0-49.5% by weight of the total oil fieldchemicals in the whole composition. More preferably the oil fieldchemicals outside the microcapsules in the composition account for 0-30%by weight of the total oil field chemicals in the whole composition.

The bulk polymer can account for 55-100% by weight of the bulk polymer,adhesive agents, property improving agents and oil field chemicalspresent in the bulk polymer. Preferably the bulk polymers account for70-100% by weight of the composition excluding the weight of themicrocapsules.

The combinations of bulk polymers, adhesive agents and propertyimproving agents can account for 0-95% by weight of the wholecomposition. Preferably the combination of bulk polymers, adhesiveagents and property improving agents can account for 20-90% by weight ofthe whole composition.

The oil field chemical can be present at 0.5 to 99.5% by weight of thetotal weight of the composition. Preferably, the oil field chemical ispresent at 5-70% of the total weight of the composition.

Multi-Micro-Reservoir Structure

The compositions provided by this invention form a multi-level physicalstructure. Bulk polymers in combination with additives form a matrix ofpredominantly bulk polymers. This matrix is present on macro scale, withthe matrix being no less than 400 micrometers in at least one dimension.The microcapsules are incorporated into the composition. No less than50.5% of total oil field chemicals within the composition are locatedinside the microcapsules.

In a composition having the oil field chemicals simply mixed with, anddistributed into, the bulk polymer, the oil field chemical is morehighly dispersed throughout the bulk polymer with a less distinctboundary due to lack of restriction, compared to a mixture ofmicroencapsulated oil field chemicals in a bulk polymer, where the oilfield chemicals are present at high concentration in the microcapsulescompared to the bulk polymer. Isolated micro-matrices are not formedwhen oil field chemicals are mixed into bulk polymers.

In the compositions provided by this invention, the microcapsules can beevenly dispersed in bulk polymers in a microcapsule. In somecompositions, the microcapsules can be non-uniformly dispersed. As aresult of embedding pre-formed microcapsules into bulk polymers, thecompositions of the present invention are much more heterogeneousmicroscopically with a distinct boundary due to the restriction providedby the structure of microcapsules. Higher concentrations of oil fieldchemicals are present within the microcapsules than outside themicrocapsules. For compositions comprising microcapsules with shells,the segregation by the shells is obvious. In compositions comprisingembedded microcapsules having a micro-matrix structure in bulk polymers,the oil field chemicals are confined in the micro-matrixes. It is alsoone aspect of the invention that the polymeric materials that form themicro-matrixes (FIG. 1d ) can be different and less permeable than thebulk polymers used for the composition. The micro-structure of themicroencapsulant can be different than that of the bulk polymers in themacro-matrix. The microcapsules can also have various complex structures(from core-shell to core-multi-shell to multicore-shell, and frommicro-matrix to micro-matrix-shell to multi-core-micro-matrix-shell).Thus the compositions of this invention have a multi-level structurewith hierarchy. From a different point of view, with reference to oilfield chemicals, each microcapsule is a micro-reservoir. Thecompositions of the present invention form a multi-micro-reservoirstructure.

The multi-micro-reservoir structure favours the controlled and sustainedrelease of the oil field chemicals within the microcapsule. In order tobe released, the microencapsulated oil field chemicals have to movethrough two distinct compositions: from within microcapsules into thebulk polymer, and then from the bulk polymer to the surrounding fluidsin the targeted hydrocarbon reservoir. The shells and/or micro-matricesof the microcapsules, which can be more dense and impermeable than thebulk polymers within the composition by design, will form the firstbarriers to the release of the oil field chemicals from withinmicrocapsules. Such a first barrier does not exist in compositions wherethe oil field chemicals are directly distributed in bulk polymers.Compositions in which the oil field chemicals are present inmicrocapsules are expected to provide for the slow and controlledrelease of the oil field chemicals.

The synergistic sustained and controlled release of the oil fieldchemicals can be further enhanced by the adhesion between themicroencapsulant and the bulk polymer phase through physical interactionand chemical reaction.

Composition Formation

Overall, the composition can be manufactured in a 2 step process. In thefirst step, microcapsules containing oil field chemicals are prepared.In the second step, the microcapsules are incorporated into bulkpolymers. The step-by-step manufacturing process used in manufacturingthe compositions of the present invention allows for the formation ofthe multi-level multi-micro-reservoir structure described above.

The step of forming a plurality of microcapsules can comprise a physicalmethod, a chemical method or a physico-chemical method. The physicalmethod can be selected from the group consisting of spray drying,fluidised bed coating, co-extrusion, and solvent evaporation.

It is preferred that microcapsules are made by spray drying a mixture ofoil field chemicals and polymers.

In another preferred method, microcapsules containing oil fieldchemicals are made by co-extrusion of two phases of polymers or mixtureof polymers. An inner phase is a mixture of a polymer or prepolymercontaining oil field chemicals. An outer phase is a mixture of a polymeror prepolymer containing either no oil field chemicals or less oil fieldchemicals than are present in the inner phase.

Microcapsules can be formed by chemical methods using one or morein-situ reactions. A preferred chemical method of this invention formsmicrocapsules by the in-situ polymerization of monomers distributed inan emulsion containing one or more oil field chemicals. The term“emulsion” is used to describe a fine dispersion of one liquid in asecond liquid in which the first liquid is not soluble or miscible. Theterm emulsion includes a microemulsion, a microsuspension, amini-emulsion as well as a normal emulsion and suspension. An emulsioncan be a discontinuous internal oil phase in a continuous water phase(O/W) or internal water phase in oil phase (W/O). The emulsion can bemore complicated with an internal phase itself being a dispersion, suchas a W/O/W or O/W/O type of emulsion. The polymerisation can occur inthe water phase, the oil phase, the interphase between water and oilphases, more than one of these phases or in all of these phases. Thusthe polymerisation can be termed emulsion polymerisation, miniemulsionpolymerisation, microemulsion polymerisation, suspension polymerisation,micro-suspension polymerisation, colloid polymerisation, interfacialpolymerisation, etc. The polymerisation can be either additionpolymerisation, such as with the use of vinyl monomers, or condensationpolymerisation, such as with the use of corresponding monomers andprepolymers. Initiators and/or catalysts and heating or high energyirradiation (e.g. UV) may be used. Examples of condensation polymers aremelamine-formaldehyde resin, phenol-formaldehyde resin,urea-formaldehyde resin, epoxy resin, urethane/urea resin, polyesterresin etc. Examples of vinyl monomers are acrylamide, acrylic acid,acrylic esters, methacrylic acid, methacrylic esters, styrene,4-vinylbenzyl chloride, divinylbenzene, methylenebisacrylamide, etc.

Microcapsules with core shell structures can be prepared by dispersingan oil field chemical, a mixture of an oil field chemical withnon-polymeric materials, or a mixture of an oil field chemical withnon-polymeric materials and monomers into small particles in the form ofan emulsion with the aid of physical force and emulsifiers. Stabilizerscan be used to stabilize the emulsions when they are formed. Monomers orprepolymers can be distributed in the interphase, the continuous phaseor in both phases. The monomers can be polymerised and deposited on thecores or other shells to form the shells. A pre formed polymer can alsobe added to the emulsions and deposited together with newly formedpolymers to form the shells. The polymer can be cured during or afterthe polymerisation process. Alternatively, monomers or prepolymers canbe deposited on the core and then the prepolymers can be cured to form apolymer coating. Oil field chemicals can also be added to the continuousphase. Overall, more oil field chemicals are present in the dispersedinternal phase than in the continuous phase.

Micro-matrix type microcapsules can also be formed by polymerisationfrom emulsions. A mixture of oil field chemicals with a highconcentration of monomers, prepolymers, a combination of monomers andprepolymers, or a combination of monomer/prepolymer and a preformedpolymer, can be dispersed to form an emulsion. Polymerisation and/orcuring (crosslinking) of monomers inside droplets or a dispersedinternal phase can form a micro-matrix containing oil field chemicals.During this process, the structure of the mixture will undergo changes.For example, at the beginning of the process, the oil field chemicalsare molecularly distributed, however at the end of the process, they canform very fine phases in the microcapsules or can still be molecularlydistributed.

The physico-chemical method can be coacervation phase separation.

By using one of the methods or combinations of the above methods,microcapsules containing oil field chemicals with structures specifiedabove can be made.

Micro-matrixes, core shell particles or micro-matrixes with shells canbe prepared beforehand. These micro particles can then be exposed to gasor liquid oil field chemicals or mixtures of oil field chemicals withnon-polymeric compounds and the oil field chemicals can be absorbedand/or adsorbed by the microparticles.

Microcapsules can be recovered as solid powders using methods includecentrifugation and/or filtration followed by drying. Drying methods caninclude evaporation of solvent or water in the air, drying in a vacuumoven or fluidised bed, etc.

Both solid and liquid oil field chemicals can be microencapsulated andrecovered as solid powders. The oil field chemicals can have differentproperties such as density, chemical nature, particle size distributionand surface properties in the case of solid oil field chemicals. Thesepowders can be incorporated into bulk polymers. The microencapsulationcan also provide protection to the oil field chemicals. Thus thisinvention provides a means to process liquid and solid oil fieldchemicals into compositions with sustained and controlled releaseproperties.

In one aspect of the invention, a composition having two or moredifferent microencapsulants can be formed by microencapsulating amicrocapsule with a core shell structure, micro-matrix structure or amicro-matrix-shell with one or more microencapsulants. As such, a doubleshell or different micro-matrix-shell structure or micro-matrix-doubleshell structure can be formed.

Besides double microencapsulation, microcapsules can be treated afterthey are formed. The treatment can be physical or chemical. For example,one or more different chemicals can be added to the emulsion systemafter the formation of the microcapsules. In such treatments, noadditional shell is formed. Rather the surface properties of themicrocapsules are altered due to adsorption or reaction at the outersurface of the pre-formed microcapsules. The chemical can have physicalinteraction, such as deposition, or chemical reaction with first formedshells or micro-matrixes. As such, the properties of themicroencapsulant can be modified for example to allow different chemicalgroups to become attached to the outer surface of the microcapsules orto enhance the stability or barrier properties of the microencapsulant.One particular chemical treatment is grafting of new polymers onto thesurface of the microcapsules.

By microencapsulating oil field chemicals and post-treating themicrocapsules using the above methods, microencapsulated oil fieldchemical with various functional chemical groups can be prepared. Thefunctional chemical groups can be reactive. Examples of such chemicalgroups can be selected from the group consisting of carboxylates,amines, quaternised amine, anhydrides, hydroxyls, isocyanates,phosphates, nitriles, esters and aldehydes, silanol, N-methylol etc.

Incorporation of Microcapsules into Bulk Polymers

A method of making a composition comprising: (a) microcapsulescomprising an oil field chemical and a microencapsulant, where themicrocapsules have an outer surface, and the oil field chemical iscontained within the microcapsules and (b) a bulk polymer, where themicrocapsules are embedded within the bulk polymer, comprises providingthe microcapsules and embedding the microcapsules within the bulkpolymer. The microcapsules can have at least one of the structuresdescribed above and shown in FIG. 1. The method can further comprise thestep of forming a plurality of microcapsules, where each microcapsulecomprises an oil field compound and one or more polymericmicroencapsulants, where the microcapsule comprises at least one of thestructures described above and shown in FIG. 1. The method can furthercomprise forming the mixture of the microcapsules and the bulk polymerinto a shaped article.

Microcapsules containing an oil field chemical are incorporated intobulk polymers to form a composition. A composition can comprise (a)microcapsules containing an oil field chemical, (b) a bulk polymer intowhich the microcapsules are homogeneously dispersed and embedded in and(c) optionally one or more additives. The bulk polymeric material canaccount for 20-98% by weight of the total mass of the composition. Themicrocapsules can account for 2-80% by weight of the total mass of thecomposition. The one or more additives can account for 0-30% by weightof the total mass of the composition.

The bulk polymer(s) used in the composition can be a commerciallyavailable polymer. The bulk polymer(s) can also be formed by directpolymerization of monomers or curing of prepolymers during themanufacture of the compositions.

One or more additives can be added to the bulk polymers to helpincorporate the microcapsules into various compositions and articles.

Oil field chemicals that have not been microencapsulated can be added tothe bulk polymers during the process to incorporate the microcapsulesinto the bulk polymers.

The compositions can be formed by any of a variety of known processesincluding, but not limited to, processes with various level ofmechanical force and shearing at different temperatures and pressures.Examples of these processes include mechanical stirring, compounding,extruding through a twin screw, a single screw compounder/extruder,casting, and injection moulding, including reaction injection moulding,which involves the rapid polymerisation of monomers/prepolymers aroundthe oil field chemical, high speed dispersing using equipment with arotor, a rotating mixer, or other method known in the art.

Compositions can be made by compounding or blending particles comprisingmicroencapsulated oil field chemicals with polymers and additives at theprocessing temperature of the bulk polymers, i.e., a temperature closeto or above the melting point or glass transition of the bulk polymers.The compounding can be carried out through a single or twin screwcompounder and/or extruder.

Compositions can also be made by mechanically dispersing particlescomprising microencapsulated oil field chemicals with monomers and/orprepolymers and initiators or curing agents. A high or low shear mixer,such as a simple mechanical stirrer, or equipment such as a SilversonDisperx stirrer can be used. The mixture can be cast or moulded, andthen polymerized or cured subsequently by changing the temperatureand/or leaving the composition to stand for a sufficient period of timeto allow curing.

In another preferred process, compositions can be made by mixing orblending microencapsulated particles comprising oil field chemicals withpolymers, additives and a dispersing solvent at low temperature.Examples of dispersing solvents are water and acetone. A high or lowshear mixing machine, such as a simple mechanical stirrer, or equipmentsuch as a Silverson machine, or a Disperx stirrer can be used. Themixture can then be cast or moulded. A final composition can be obtainedby evaporating the dispersing solvents.

The above described process can be used individually or in combination.

Reactions in the Process to Incorporate Microencapsulated Particles intoBulk Polymer(s)

During the process of manufacturing the composition, no reactions occurthat form chemical bonds between the oil field chemicals and anypolymers used in making the composition. However, reactions among anycomponents of the composition other than the oil field chemicals, arenot excluded.

The microcapsules can be incorporated into bulk polymers by physicalprocesses such as mixing and blending. During these processes,conditions such as temperature and pressure are controlled. In this wayreactions between the bulk polymers and the oil field chemicals are notexpected to occur.

The compositions can comprise microcapsules where the outer surfaces ofthe microcapsules are not reactive with the bulk polymer. Thecompositions can comprise microcapsules where the outer surfaces of themicrocapsules comprise one or more reactive groups that are reactivetowards the bulk polymer. The reactive groups can be selected from thegroup consisting of carboxylates, amines, anhydrides, hydroxyls,isocyanates, phosphates, nitriles, esters, aldehydes, silanols,N-methylol, etc. The composition can comprise one or more chemicalgroups on their surface that are reactive towards the bulk polymer,where the reactive groups are selected from the group consisting ofcarboxylates, amines, anhydrides, hydroxyls, isocyanates, phosphates,nitriles, esters, aldehydes, silanols and N-methylol.

During the process of incorporating microcapsules into the bulkpolymers, reactions between the polymeric microencapsulant and the bulkpolymers can occur.

Articles

The composition can be formulated for use in a hydrocarbon reservoir.The composition can be in the form of an article configured forplacement in a hydrocarbon reservoir. The article can be in any one of avariety of shapes including a rod, a bar, an oval, a cuboid, a strip, astrand, a disc, a button, a block, a cylinder, a flat piece, a net, anda film. The shape of the article can be modified to adjust the surfacearea of the articles that will be exposed to reservoir fluids. Forexample, a bar or strip can contain one or more grooves to increase thesurface area of the article. The grooves can have any number of shapes,preferably V-shaped or semi-circular. Preferably, the objects are >400micrometer in at least one dimension.

The articles can be formed as part of the process that forms thecomposition, i.e., a forming process coupled with the process toincorporate microcapsules into bulk polymers. For example, in aninjection moulding process, the microcapsules, the bulk polymer formingprepolymers or monomers, initiators or curing agents and additives canbe mixed directly at a mould.

The articles can also be formed in one or more steps after thecomposition is formed. For example, a composition comprisingmicrocapsules and bulk polymers/additives can be prepared through acompounding process to form the composition in a twin extruder. Thecompounded materials can then be processed through a single screwextruder to form articles such as strips, bars, rods, films or rolls.The strips, bars, rods, films and rolls may be further granulated toform balls, granules, etc.

The articles comprise a mixture of microcapsules comprising one or moreoil field chemicals and one or more bulk polymers, where the articleshave a defined shape. The articles can be formed by any of a variety ofknown processes including, but not limited to compounding, extruding,thermo-forming, non-thermo forming, casting, and injection moulding,including reaction injection moulding, which involves the rapidpolymerisation of monomers/prepolymers around the oil field chemical.Some preferred processes are described below.

The articles can be thermoformed by extruding a mixture comprisingmicrocapsules containing one or more oil field chemicals within themicrocapsules and one or more bulk polymers through a single or twinscrew compounder and/or extruder. Articles can be formed into thedesired shapes by casting a mixture of the microcapsules, adhesiveagents, embedding prepolymers, additives and initiators or catalystsinto a mould and polymerizing the mixture. Articles can also be formedinto the desired shapes by casting mixtures of the microcapsules,adhesive agents, embedding polymers and additives or prepolymers andinitiators or catalysts, additives, and solvent into a mould, allowingthe solvent to evaporate, and/or polymerizing the mixture. Articles canalso be formed into the objects of the desired shapes by casting themicrocapsules, adhesive agents, embedding prepolymers, additives andinitiators or catalysts onto the location where the article is desiredto be fixed, and polymerizing the article in-situ.

Microencapsulated tracers and well treatment agents can be formed intoarticles comprising various bulk polymers such as epoxy resins, vinylester resin, polyurethanes, polyesters, acrylic polymers oracrylonitrile-butadiene-styrene, as described above. Preferably thecompositions and articles are solid and are in the shape of a rod, abar, an oval, a cuboid, a strip, a strand, a disc, a button, a cylinder,a bead, a ball, a block, a flat piece, a film or a net. Articlesproduced by casting can contain the oil field chemicals in amounts of upto 70% by weight of the article.

Articles can be made by a process comprising the following steps: (a)blending the microcapsules with adhesive agents, embedding polymers andadditives to form a mixture, and (b) forming the mixture into one ormore shaped objects. The process can further comprise one or both of thefollowing steps: formulating and/or pre-treating one or more oil fieldchemicals, and forming a plurality of microcapsules, where eachmicrocapsule particle comprises a core comprising at least one oil fieldchemical, and at least one shell that at least partially covers thecore.

Articles can also be made by a process comprising the following steps:(a) blending the microcapsules and adhesive agents together withembedding prepolymers and/or monomers, additives and initiators orcatalysts, and (b) forming the mixture into one or more shaped objects.The process can further comprise one or both of the following steps:formulating and/or pre-treating one or more oil field chemicals, andforming a plurality of microcapsules, where each microcapsule particlecomprises a core comprising at least one oil field chemical, and atleast one shell that at least partially covers the core.

Articles can also be made by a process comprising the following steps:(a) blending the microcapsules and adhesive agents together with anembedding polymer, or prepolymers and/or monomers, additives andinitiators or catalysts, and solvents, (b) forming the mixtures into oneor more shaped objects. The process can further comprise one or both ofthe following steps: formulating and/or pre-treating one or more oilfield chemicals, and forming a plurality of microcapsules, where eachmicrocapsule particle comprises a core comprising at least one oil fieldchemical, and at least one shell that at least partially covers thecore.

A hydrocarbon reservoir monitoring system can comprise a compositioncomprising: (a) microcapsules comprising an oil field chemical and amicroencapsulant, where the microcapsules have an outer surface, and theoil field chemical is contained within the microcapsules, and (b) a bulkpolymer, where the microcapsules are embedded within the bulk polymer.The compositions can be placed at various locations in a hydrocarbonreservoir and/or a well penetrating the reservoir. The hydrocarbonreservoir monitoring system can further comprise a means of obtaining asample of a fluid from a hydrocarbon reservoir. Means of obtainingsamples or a sample of a fluid from a hydrocarbon reservoir are wellknown to one of ordinary skill in the art. The means include devicesthat can manually or automatically collect samples from the fluidproduced from the well penetrating the reservoir.

Preparation of Articles from Microencapsulated Solid or Liquid Oil FieldChemicals of Different Physical States and Properties and Homogeneity ofthe Final Articles

The methods described herein were used to formulate both solid andliquid oil field chemicals having different properties, such as densityand reactivity, into final articles that could be deliverable tohydrocarbon reservoirs. This is shown in the Example cited below.

Tracers having different physical states and properties and a biocidewere separately microencapsulated into powders. These powders wereincorporated into bulk polymers (epoxy resin, polybutylene terephthalateor polypropylene) to form articles that were evaluated to determinetheir release properties. The properties of these articles were comparedwith comparable articles in which the pure tracer or the biocide (not ina microencapsulated form) were mixed with a bulk polymer.

Pure tracer was incorporated into epoxy resin and cast into articles inthe shape of solid cylinders (Comparative Example 1, 3, 9-12). Attemptsto cast cylinders from pure tracer D and epoxy resin failed due totracer D being a heavy liquid with a density of 2.0 g/cm³ and therebeing little adhesion between the epoxy resin and the tracer(Comparative Example 12). When pure biocide A was mixed with epoxy resinand cured at 60° C., a dark brown/black colour was observed (ComparativeExample 11). It was determined that the colour was caused by reactionbetween the biocide and epoxy resin. The reaction destroyed the biocideand made the biocide un-releasable. Such a cylinder was not a sustainedrelease composition.

Tracer D and biocide A were readily microencapsulated and free flowingsolid powders comprising microcapsules containing the tracer or thebiocide were recovered (Examples 11, 13). The powders were easilydispersed in epoxy resin and the microcapsules were preserved duringcuring of the resin. There was good adhesion between the microcapsulesand epoxy resin due to physical interaction and reaction between thechemical groups at the outer surface of the microcapsules (carboxylate,N-methylol and amine) and epoxy resin. These cylinders provided for thesustained release of tracer from the microcapsule (Examples 12, 14). Thecylinder made of microencapsulated biocide A and epoxy resin showed onlyvery light yellow colour coming from the biocide itself, indicating thereaction between the biocide and epoxy resin was prevented.

Tracers A, B and C were solids at room temperature but each of thesetracers had different densities. Each of these tracers was able to bemixed with epoxy to form cylinders. However, significant inhomogeneitywas seen in the cast cylinders (Comparative Examples 1, 3, 9, 10).Tracers A and C tended to settle to the bottom of the cylinders due totheir high densities. Fumed silica, a commonly used thickener, was usedin some of the compositions to aid in improving the distribution of thetracer in the articles (Comparative Examples 3 and 4) but resulted inlimited success.

Tracers A, B and C were microencapsulated and free flowing powders wereobtained (Examples 1, 4, 7). The free flowing powders were readilyformulated with epoxy resin and good adhesion between the microcapsulesand epoxy resin prevented settling of the particles during the curingprocess. Cylinders having high homogeneity throughout were cast fromthese microencapsulated tracers (Example 2, 15, 16). These cylindersprovided for the sustained release of the encapsulated tracer.

Tracer Biocide Oil field chemicals A B C D A Physical States of Oilfield Solid Solid Solid Liquid Solid chemicals at Room TemperatureDensity of Oil field chemicals at 2.4 1.2 3.0 2.0 ~1.3 Room Temperature,g/cm³ Availability in Casting Pure Oil Yes Yes Yes No, No, fieldchemicals with Epoxy Resin due to due to liquid state reactivityDimensional Homogeneity of No, Yes No, N/A N/A Pure Oil fieldchemicals/Epoxy due to due to Resin Cast Pieces tracer tracer settlingsettling Integrity of Pure Oil field No Not Not N/A N/A chemicals/EpoxyResin Cast tested tested Pieces During Long Term ElutionMicroencapsulation into Powders Yes Yes Yes Yes Yes Availability inCasting Yes Yes Yes Yes Yes Microencapsulated Oil field chemicals withEpoxy Resin Dimensional Homogeneity of Yes Yes Yes Yes YesMicroencapsulated Oil field throughout throughout throughout throughoutthroughout chemicals/Epoxy Resin Cast Pieces Integrity ofMicroencapsulate Oil Yes Not Not Not Not field chemicals/Epoxy ResinCast tested tested tested tested Pieces During Long Term Elution

When tracer A was formed into a cylinder using epoxy resin, the cylinderhad a high degree of inhomogeneity due to settling of the tracer. Theaddition of fumed silica delayed settling and resulted in a morehomogeneous product. A product obtained by casting microencapsulatedtracer A with epoxy resin was the most homogeneous.

A cylinder cast from microencapsulated tracer A showed a very lightyellow/brown colour caused by the distribution of a small amount of freetracer into epoxy resin. The very light colour of microencapsulatedtracer/epoxy resin is a sign that most of the tracer remainedconcentrated inside the microcapsules within the cast epoxy. This is inagreement with the concept of a multi-micro-reservoir structure existingin the compositions and articles of this invention.

Cast cylinders with tracer A and epoxy resin were placed in differenteluents at 60° C. Better mechanical integrity of cast cylinders wasobtained by microencapsulation of the tracer and mixing themicrocapsules with epoxy resin. In toluene at 60° C. (simulating higharomatic light oil at a temperature representative of a hydrocarbonreservoir), cylinders made of (a) pure tracer A/epoxy and (b) puretracer A/fumed silica/epoxy resin both showed cracks after about 5 daysand 2 weeks, respectively (Comparative Example 2 & 4). However, themicroencapsulated tracer A/epoxy cylinder remained intact after 4500hours in toluene (Example 2).

The improved integrity in the microencapsulated tracer A/epoxy resincylinder indicates there is good adhesion between the shells of themicroencapsulated tracer and the epoxy resin due to physical interactionand chemical reaction between chemical groups at the outer surface ofthe microcapsules and epoxy resin. The combination of the physicalinteraction and the chemical reaction between the outer surface of themicrocapsules and the epoxy resin, with the multi-micro-reservoirstructure of the microencapsulated particles, makes the microencapsulanta more effective barrier for microencapsulated oil field chemicals torelease than the microcapsules are used alone, thus helps to achievesynergistic control and sustained release shown below.

As further examples, microencapsulated tracers B and C were compoundedwith bulk polymers to form articles in the form of strips that providedfor sustained release of the tracers when the strips were eluted in asynthetic oil.

Release of Oil Field Chemical from Compositions and Articles

The various compositions and articles described herein provide differentrelease rate profiles as shown below in the Examples. While there is noindustry accepted standard method for testing release rates, one ofordinary skill in the art would recognize that typical dissolution typetesting at elevated temperatures representing those found in ahydrocarbon reservoir using an eluent representative of an oil can beused. Typical dissolution type testing involves placing a materialcontaining a compound of interest into an eluent with stirring, takingsamples of the eluent at various times and determining the amount of thecompound of interest that is present in the eluent over time. From thisinformation, a graph of the cumulative amount of the compound ofinterest released over time can be produced. Comparisons of length oftime needed to release a desired amount of compound of interest can bemade based on the profile of the data.

The release profile can be dependent on the eluent selected. For mostoil tracers, the lower the molecular weight and/or the more aromatic theeluent is, the faster the release of the tracer into the eluent will be.For example, using a low molecular weight aromatic compound, such astoluene, as an eluent usually results in the rapid release of organicsoluble tracers. However, in real oil, e.g. crude oil or synthetic oil,the release rate can be much lower. While synthetic oil can be used tosimulate the release of tracers to crude oil, material having a higheraromatic content, such as toluene, can be used in rapid screening.

Examples 1-2 and 10 show that under conditions in a dissolution testperformed at 60° C. using an eluent that simulates reservoir fluid thatthe following compositions provided the following releases:

Composition Eluent Release Pure Tracer Synthetic 100% in about 2 minutesOil Encapsulated Synthetic About 50% in about 4-5 hours Tracer Oil PureTracer Toluene About 30% in about 43 hours (1.8 days) in Bulk About 50%in about 100 hours (4 days) and Polymer About 90% in about 714 hours (30days) Encapsulated Toluene About 20% in about 115 hours (68 days) andTracer in About 30% in about 3285 hours (136 days) Bulk PolymerEncapsulated Synthetic About 0.1% in 4500 hours (187 days) Tracer in OilBulk Polymer

The release of the microencapsulated tracer was approximately linearover time, indicating that the release rate is relatively constant andhighly controlled. This is an important feature that is in demand by theindustry. The controlled release of the tracer is a result of thepresence of a multi-micro-reservoir structure in the compositions andarticles of the current invention. Both the bulk polymer and the shellencapsulating the oil field chemicals provide barriers that resist theinfiltration of reservoir fluids into the core, retarding the release ofthe oil field chemicals. As is shown below, the retardation of therelease of the oil field chemicals from articles described herein ismuch greater than expected from the combination of the two barriersbased on the combined individual release rates. This effect can beconsidered to be synergistic. The multitude of micro-reservoirs of oilfield chemicals in the compositions ensures a consistent sustainedrelease of the compounds from the articles over time.

Surprisingly, the combination of the encapsulated tracer in the bulkpolymer greatly slows the release of the tracer. It was unexpected thatthe combination of the encapsulated tracer in the bulk polymer wouldslow the release of the oil tracer so that only less than 0.1% of thetotal tracer was released over 187 days of time in synthetic oil,especially when the encapsulated tracer provided about 50% release overa period of only 4-5 hours and the combination of the tracer in the bulkpolymer provided about 30% release in about 1.8 days. Even in toluene,one of the fastest eluting eluents, only about 20% and 30% of theapplied microencapsulated tracer was released over about 68 and 136days, respectively.

The articles described herein can provide for the release of an oilfield chemical into eluents representative of oil under the testconditions described herein such that measureable concentrations of theoil field chemical can be obtained in the eluent for at least 6 months,preferably at least 9 months, more preferably at least 1 year, even morepreferably at least 15 months, particularly at least 18 months, moreparticularly at least 21 months, even more particularly at least 2years, especially at least 27 months, more especially at least 30months, even more especially at least 33 months, and most preferably atleast 2 years after the article has been placed in the test system.

The articles described herein can provide release of the oil fieldchemical into eluents representative of oil (or reservoir fluid) underthe test conditions described herein such that ≤ about 45%, preferably ≤about 40%, more preferably ≤ about 35%, even more preferably ≤ about30%, particularly ≤ about 25%, more particularly ≤ about 20%, even moreparticularly ≤ about 15%, especially ≤ about 10%, more especially ≤about 5%, or even more especially ≤ about 1% of the applied oil fieldchemical is released into the eluent over about 68 days.

The articles described herein can provide release of the oil fieldchemical into eluents representative of oil under the test conditionsdescribed herein such that ≤ about 30%, preferably ≤ about 25%, morepreferably ≤ about 20%, even more preferably ≤ about 15, particularly ≤about 10%, more particularly ≤ about 5%, or even more particularly ≤about 1% of the applied oil field chemical is released into the eluentover about 136 days.

The articles described herein can provide release of the oil fieldchemical into eluents representative of oil under the test conditionsdescribed herein such that that ≤ about 20%, preferably ≤ about 15, morepreferably ≤ about 10%, even more preferably ≤ about 5%, particularly ≤about 1% or more particularly ≤ about 0.5% of the applied oil fieldchemical is released into the eluent over about 180 days.

Preferably, the articles described herein can provide release of the oilfield chemical into eluents representative of oil under the testconditions described herein such that that less than 50% of the oilfield chemical can be released into the eluent over a period at least 6months, preferably at least 9 months, more preferably at least 1 year,even more preferably at least 15 months, particularly at least 18months, more particularly at least 21 months, even more particularly atleast 2 years, especially at least 27 months, more especially at least30 months, or even more especially at least 33 months after the articlehas been placed in the test system. Some articles can provide for therelease of an oil field chemical for preferably at least 2 years, morepreferably at least 5 years, even more preferably at least 10 years, atleast 15 years or most preferably more than 20 years after the articlehas been placed in the test system.

The articles described herein can provide release of the oil fieldchemical into the oil well fluids in a hydrocarbon reservoir such thatmeasureable concentrations of the oil field chemical can be obtained forat least 6 months, preferably at least 9 months, more preferably atleast 1 year, even more preferably at least 15 months, particularly atleast 18 months, more particularly at least 21 months, even moreparticularly at least 2 years, especially at least 27 months, moreespecially at least 30 months, even more especially at least 33 monthsafter the article has been placed in a hydrocarbon reservoir. Some ofthe articles can provide release of the oil field chemical into the oilwell fluids in a hydrocarbon reservoir such that measureableconcentrations of the oil field chemical can be obtained for at least 3years, preferably at least 5 years, more preferably at least 10, mostpreferably at least 20 years after the article has been placed in ahydrocarbon reservoir.

The composition can release at one of the following percentages of theapplied dose of tracer present in the microcapsule over a period of 45days at 60° C. in a fluid representing an oil field fluid: <45%,preferably <40%, more preferably <30%, even more preferably <25%,particularly <20%, more particularly <15%, even more particularly <10%,especially <5%, more especially <1% and even more especially <0.5%.

Use of Articles Providing a Sustained Release in Well Reservoirs

The compositions described herein have numerous applications in the areaof detecting and tracing the movement of oil field fluids in ahydrocarbon reservoir. The compositions and articles described hereincan be used in monitoring/tracing a flow of fluid from a hydrocarbonreservoir. The compositions comprising encapsulated tracer particles andone or more bulk polymers in the form of articles of strips, bars, nets,etc. can be placed or delivered downhole to near well bore positionsrelative to well casings. Ingress and in-flow of gas, oil, water ormixtures of oil and water can be detected and monitored.

A method of tracing fluid flow from a hydrocarbon reservoir can comprisethe steps of placing within a well penetrating the reservoir acomposition of the first aspect of the invention, where the oil fieldchemical is a tracer, collecting one or more sample of fluids flowingfrom the well and analysing said sample to determine at least one of thepresence or absence of the tracer and the concentration of one or moretracers in fluids flowing from the well. The method can further compriseone or more of the following steps: collecting a plurality of samples offluids flowing from the well over time, analyzing the samples anddetermining the presence or absence of the tracer in the sample, andanalyzing the samples and determining the concentrations of one or moretracers in the reservoir fluids over time. The composition can be placedat, around or within a fracture in a rock formation forming saidreservoir or at around or within a bore hole, or within, or attached to,a well completion apparatus installed within the well. The step ofplacing the composition within a well penetrating the reservoir cancomprise in-situ polymerization.

Methods used to monitor/trace a flow of fluid from a hydrocarbonreservoir comprise the following steps: (a) placing shaped compositioncomprising a mixture of a bulk polymer and microcapsules comprising atracer compound and a polymeric microencapsulant or a tracer containedin a three-dimensional polymeric matrix, on, or in, pipes or fittings tobe inserted into a well, to locations on a well, such as filters, casingnear or part of the well bores, or within, or attached to, other wellcompletion apparatus installed within the well, (b) thereaftercollecting a sample of fluid flowing from the well and analysing thesample to determine the presence or absence of the at least one tracerand optionally determining the concentration of one or more tracers influids flowing from the well, (c) collecting and analysing a pluralityof samples of fluids flowing from the well over a period of time anddetermining the concentrations of one or more tracers in the reservoirfluids, and (d) analysing the concentrations of the tracer to determinea pattern of back flow to obtain further reservoir flow information.

Another method of monitoring/tracing a flow of fluid from a hydrocarbonreservoir comprises the following steps:

(a) forming a shaped composition from microcapsules comprising one ormore tracers, an embedding polymer or prepolymers with catalysts andadditives, on, or in, pipes or fittings to be inserted into a well, atone or more locations of a well, such as filters, casing near or part ofthe well bores, or within, or attached to, other well completionapparatus installed within the well, and

(b) collecting a sample of fluid flowing from the well and analysing thesample to determine the presence or absence of the at least one tracerand optionally determining the concentration of one or more tracers influids flowing from the well, or

(c) collecting and analysing a plurality of samples of fluids flowingfrom the well over a period of time and determining the concentrationsof one or more tracers in the reservoir fluids, and analysing theconcentrations of the tracer to determine a pattern of back flow toobtain further reservoir flow information.

Compositions containing microcapsules of tracer can be used to placetracer into well pipes using in-situ polymerisation. In-situpolymerisation can be used to place tracer within pipes in a hydrocarbonreservoir when the pipes are already partially installed. A compositioncomprising microcapsules of tracer can be mixed with a component in atwo-part polymer system, such as a two-part epoxy resin. Epoxy coatingsare generally packaged in two parts that are mixed prior to application.The two parts consist of 1) an epoxy resin which is to be cross-linkedwith 2) a co-reactant or hardener. A composition comprisingmicrocapsules of tracer can be mixed with the epoxy resin componentwhich then becomes mixed with a co-reactant or hardener when thetwo-part system is applied to holes within pipe screens located withinpipes in the reservoir. In some two part systems, the resin and thehardener are applied as separate materials and then mixed. In othersystems, the two components are provided in separate tubes and are mixedtogether in a single nozzle when applied.

A further method of monitoring/tracing a flow of fluid from ahydrocarbon reservoir comprises the following steps:

(a) placing the shaped composition comprising a mixture of microcapsulescomprising one or more tracers, an embedding polymer or prepolymers andcatalysts and additives, during the drilling or completion stages, tolocations of a reservoir formations, and

(b) collecting a sample of fluid flowing from the well and analysing thesample to determine the presence or absence of the at least one tracerand optionally determining the concentration of one or more tracers influids flowing from the well, or

(c) collecting and analysing a plurality of samples of fluids flowingfrom the well over a period of time and determining the concentrationsof one or more tracers in the reservoir fluids, and analysing theconcentrations of the tracer to determine a pattern of back flow toobtain further reservoir flow information.

In a manner similar to handling tracers, other types of oil fieldchemicals, such as well treatment agents, can be placed or delivered tonear well bore positions of well casing and/or reservoir formations toprovide well treatment or intervention. A method of treating ahydrocarbon reservoir penetrated by a well can comprise the step ofplacing within a well penetrating the reservoir a compositioncomprising: (a) microcapsules comprising an oil field chemical containedwithin the microcapsules, where each microcapsule has an outer surface,and (b) a bulk polymer, where the microcapsules are embedded within thebulk polymer, and the oil field chemical is a well treatment agent. Themethod can further comprise one or more of the following steps:collecting samples of fluids flowing from the well over time, analyzingthe samples and determining the presence or absence of the targetedchemical compound in the sample, and analyzing the samples anddetermining the efficiency of the treatment over time. The compositioncan be placed at, around or within a fracture in a rock formationforming the reservoir or at around or within a bore hole, or within, orattached to, a well completion apparatus installed within the well. Thestep of placing the composition within a well penetrating the reservoircan comprise in-situ polymerization.

An encapsulated biocide can be formulated with one or more bulk polymersand shaped into articles. The articles in the form of strips, bars, netsetc. can be placed in or near well bore positions relative to wellcasings. In another aspect, the articles in the forms of bars, blocksand balls are formulated within a stimulation fluid and can be delivereddownhole to reservoir formations.

The reservoir formation being treated and analysed in the above methodscan be fractured. The compositions described herein can also bedelivered to the fractured formations within a liquid. Thus thecompositions described herein can be formulated into a fluid (such as astimulation fluid or a flooding fluid for primary and secondary oilrecovery). The compositions described herein can also be mixed withproppants or incorporated into proppants. The microcapsules can be addedinto the interior of a proppant and the proppant can then be coated witha polymer that acts as a shell around the core. In all these cases, therelease of the tracer from the compositions is used to trace fluidmovements associated with various operations associated with frackingand stimulation, and the release of well treatment agents, such ascorrosion inhibitors and biocides, is used to provide protection todownhole pipeline and equipment and assurance of flow within thepipelines.

Compositions comprising microcapsules comprising oil field chemicals(i.e. tracers or well treatment agents) can be used to place welltreatment agents in reservoirs and/or well pipes and provide for thesustained release of well treatment agents of periods of time from overa period at least 6 months, preferably at least 9 months, morepreferably at least 1 year, even more preferably at least 15 months,particularly at least 18 months, more particularly at least 21 months,even more particularly at least 2 years, especially at least 27 months,more especially at least 30 months or even more especially at least 33months after the article has been placed in the test system. Somesystems can release for at least 2 years, preferably at least 5 years,more preferably at least 10 years, even more preferably at least 15years, most preferably for more than 20 years, after the article hasbeen placed in the test system.

The compositions and articles described above can comprise a single oilfield chemical where the compositions and articles provide for at leasttwo different release profiles of the oil field chemical. For example, acomposition or an article can comprise a microcapsule particle embeddedin a bulk polymer, where a single oil field chemical is encapsulatedwithin the core of the microencapsulated particle and is also placedwithin the outer shell. The oil field chemical in the outer shellprovides for a rapid release (days to weeks) of the oil field chemical.The combination of the microcapsules with the bulk polymer provides aslower release (months to a year or more) of the oil field chemical. Ina further example, a composition or an article comprises a microcapsuleparticle embedded in a bulk polymer, where a single oil field chemicalis present within the bulk polymer and is also encapsulated within thecore of the microencapsulated particle. The combination of themicrocapsule with the bulk polymer provides a slower release (months toa year or more) of the oil field chemical, while the bulk polymerprovides for release at a different (e.g. more rapid, days to weeks)rate for the oil field chemical.

The compositions and articles described above can comprise two or moreoil field chemicals where the compositions and articles provide for atleast two different release profiles. For example, a composition or anarticle can comprise a microcapsule embedded in a bulk polymer, where afirst oil field chemical is present within the outer shell and a secondoil field chemical is encapsulated within the core of the microcapsule.The microcapsule in combination with the bulk polymer provides a slowerrelease (months to a year or more) for the second oil field chemical,while the outer shell in combination with the bulk polymer provides forrelease at a different (e.g. more rapid, days to weeks) rate for thefirst oil field chemical. In a further example, a composition or anarticle can comprise a microcapsule embedded in a bulk polymer, where afirst oil field chemical is present within the bulk polymer and a secondoil field chemical is encapsulated within the core of the microcapsule.The microcapsule in the combination with the bulk polymer provides aslower release (months to a year or more) for the second oil fieldchemical, while the bulk polymer provides for release at a different(e.g. more rapid, days to weeks) rate for the first oil field chemical.

The delivery of tracers in the compositions of the invention provide forthe sustained release of the tracer that allows fluid flow within andfrom a hydrocarbon reservoir and well to be monitored and traced. Amethod of providing controlled slow release of an oil field chemical toa well or hydrocarbon reservoir comprises placing a composition of thefirst aspect of the invention within an oil well or reservoir, where theoil field chemical is a well treatment agent.

In one aspect of the invention, compositions and articles comprising aplurality of tracers are placed at different locations along the lengthof a well penetrating a reservoir, during completion of the well beforeproduction begins. The article or composition at each location can beattached to a section of pipe before it is placed at that location ordelivered into the location on perforated casing. When productionbegins, detection and quantification of the individual tracers in theoil or gas produced by the well provides ways to monitor and quantifythe oil or gas being produced from different zones of the reservoir.

In another aspect of the present invention, more than one tracer can beused to measure multiple operations in the same well. For example, oilwells often have more than one producing strata or zone. A stratum couldbe fractured using a first tracer and a different stratum could befractured using a second tracer. Horizontal drilling allows for thedrilling of multiple bores terminating in a common bore which connectsto the surface. In multilateral wells such as these, several differenttracers could be used to keep track of concurrent recovery of materialsfrom the several legs (lateral bores) of such wells. These methods canbe used to monitor and track the flow of fluid from such wells.

EXAMPLES Example 1.—Preparation of Microcapsules Containing a Tracer andElution of Pure Tracer and the Tracer from Microcapsules

A tracer (Tracer A: a solid haloaromatic compound, density 2.3 g/cm³ at25° C. and 1 atm) was ground and filtered through a 100 μm sieve. 1.2 gcarboxylmethylcellulose sodium salt (Sigma) was dissolved in 78.3 gwater and then mixed with 15.9 g Beetle resin (BIP) and 0.35 g formicacid (96%, Sigma) to form an aqueous mixture. The aqueous mixture wasstirred at 25° C. for 1 hour. 60 g of the sieved tracer and the aqueousmixture were then homogenised together for 5 minutes using a SilversonL4R laboratory homogeniser. During the homogenisation process, 300 gwater was added to dilute the mixture. The homogenised mixture wasstirred at 25° C. for 2 hours and then at 65° C. for 2 more hours. Theresultant dispersion was filtered, dried in air for 3 days and thendried in a vacuum oven at 50° C. for 8 hours. The dried powder productcontaining the encapsulated tracer was filtered through a 425 μm sieve.Total tracer content in the final powder product was 84%. The powderswere dispersed in deionised water and tested using a Malvern Mastersizer2000 under 85% ultrasonication for particle size. The measured volumeweighted mean particle size was 23 μm.

Samples of the pure (not microencapsulated) tracer (0.135 g) and themicroencapsulated tracer (0.16 g, weight equivalent to 0.135 g tracer)were placed into separate samples of 18 g of a synthetic oil (80%Transulate transformer oil (a blend of highly refined mineral oils withmultifunctional additives) (Smith & Allan) and 20% Downtherm Q oil (amixture of diphenylethane and alkylated aromatics) (Dow Chemical), amodel oil representative of fluid from an hydrocarbon reservoir, at 60°C. and stirred. Samples of the synthetic oil were taken at various timesand analysed to determine the % of the applied amount of tracer releasedinto the synthetic oil. FIG. 2 shows that the pure tracer completelydissolved in the synthetic oil in just two minutes. The release of thetracer from the microcapsules was much slower, with about 50% of thetracer released at about four to five hours and about 70% of the tracerreleased at about 6 hours. The release of the tracer from themicrocapsules appears to be linear over the six hours of analysis duringwhich about 70% of the tracer was released.

Example 2—Preparation of Sustained Release Articles withMicroencapsulated Oil Tracer

A mixture of 10 g microencapsulated oil tracer particles obtained fromExample 1, 9 g bisphenol A diglycidyl ether (Sigma) and 1 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cylindrical shape with a radius of 0.9 cm and aheight of 1.1 cm. The moulded composition was cured in an oven at 60° C.for 2 hours. The articles in the shape of a cylinder were easily removedfrom the moulds. The articles contained 41% by weight of tracer A. Thecylinder appeared to be uniform throughout and showed only a very faintcolour.

Example 3—Elution Test of an Oil Tracer from Sustained Release Articlesinto Toluene

Toluene was used as a model oil for characterising the elution of tracerfrom articles in the shape of cylinders. A cylinder made from Example 2(mass: 3.4705 g) was suspended in a glass bottle containing 150 mL oftoluene. Toluene and the cylinder were stirred at a temperature of 60°C. and samples (˜0.5 mL) of toluene were taken from the bottle atvarious times. The samples were diluted, if necessary, and analysedusing GC-MS or GC-ECD. In order to maintain the total amount of toluenein the test bottle, ˜0.5 mL of fresh toluene was injected into the testbottle each time after a sample was taken.

The entire amount of toluene inside the test bottle was also replacedwith fresh toluene at various times. The cumulative concentration oftracer released was calculated by adding the concentration of the tracerin the toluene in the bottle that is mixed with the article to the finalconcentrations of tracer in toluene that had been replaced. Based on thecumulative concentration of tracer in toluene, the total amount oftracer released was calculated.

The cylinders showed excellent integrity. The morphology of the cylinderremained unchanged after 4500 hours in toluene at 60° C.

The elution profile of tracer from the cylinder containingmicroencapsulated tracer from Example 2 is shown in FIG. 3. Thecomposition provides for a sustained release with a linear release ofthe tracer after an initial release phase. The release rate was 1.94 mgtracer every 24 hours for a period of about 6 months. Only about 30% ofthe applied tracer had been released by about 5-6 months.

Example 4—Preparation of Microcapsules Containing a Second Oil Tracer

A second oil tracer (Solid tracer B: a haloaromatic compound, density1.2 g/cm³ at 25° C. and 1 atm) was sieved through a 100 μm sieve. 7.7 gcarboxylmethylcellulose sodium salt (Sigma) was dissolved in 900 g waterand then mixed with 101.8 g Beetle resin (BIP) and 2.24 g formic acid(96%, Sigma) to form an aqueous mixture. The aqueous mixture was stirredat 25° C. for 1 hour.

640 g of the sieved tracer and the aqueous mixture were then homogenisedtogether for 15 minutes using a Silverson L4R laboratory homogeniser.During the homogenisation, 300 g water was added to dilute the mixture.The homogenised mixture was stirred at 25° C. for 2 hours and then at65° C. for 2 more hours. The resultant dispersion was filtered, dried inthe air for 3 days and then dried in a vacuum oven at 50° C. for 8hours. The dried powder product was filtered through a 425 μm sieve.Total tracer content in the final powder product was 85%.

Example 5—Preparation of Slow Release Pieces Formed by Compounding andInjection Moulding with a Microencapsulated Second Oil Tracer

600 g of microencapsulated tracer particles from Example 4 werecompounded with 1.8 kg of polybutylene terephthalate (Arnite T08 200DSM) and extruded through a twin screw extruder (Prism TS24EThermoFisher) at 240° C. The extrudate was cooled with water and thenpelletized. The pellets were then dried at 110° C. for 3 hours. Thedried pellets were then injection moulded into articles havingdimensions of 125 mm long, 12.5 mm wide and 3.2 mm thick using aninjection moulding machine (Boy 22S BOYS Machines.) at 240° C.

Example 6—Elution Test of Sustained Release Articles Containing a SecondOil Tracer in a Synthetic Oil

A synthetic oil composed of 80% Transulate transformer oil (Smith &Allan) and 20% Downtherm Q oil (Dow) was used as a model oil to test theelution performance of the injection moulded articles made from Example5. A sample (0.7107 g) from the injection moulded article was suspendedin a glass bottle containing 200 mL of the above mentioned syntheticoil. The solution of synthetic oil and the cylinder was stirred at atemperature of 60° C. The procedures for taking samples and changingoils were similar to that described in Example 3.

The elution profile of the microencapsulated tracer based test piecesfrom Example 6 is shown in FIG. 4. The release of the tracer from theinjection moulded articles comprising the microencapsulated tracer wassustained compared to the release of tracer that was notmicroencapsulated as shown in Comparative Examples 5 and 6 describedbelow. The compositions containing microencapsulated tracer releasedabout 40% of the initial amount of tracer present over 49 days, whileComparative Examples 5 and 6 released about 35% of the initial amount oftracer with 2 days and between about 75% and 85% from about 9 daysthrough 49 days. The release of tracer from the article containing themicrocapsules had an initial release of about 20% of the applied doseover the first four days, followed by an approximately linear release ofabout 20% of the applied dose over the next 45 days.

Example 7—Microencapsulation of Third Oil Tracer

A third oil tracer (Tracer C: a solid halogenated benzene tracer,density 3.0 g/cm³ at 25° C. and 1 atm) was ground and sieved through a100 μm sieve. 640 g of the sieved oil tracer was microencapsulatedfollowing the procedure outlined in Example 4. The powders weredispersed in deionised water and tested using a Malvern Mastersizer 2000under 85% ultrasonication for particle size. The measured volumeweighted mean particle size was 10.5 μm. The total tracer content in thefinal powder product was 88%.

Example 8—Preparation of Sustained Release Articles by Compounding andInjection Moulding with the Third Microencapsulated Oil Tracer

600 g of microencapsulated tracer particles from Example 7 werecompounded with 1.68 Kg isotactic polypropylene (Moplen HP556E,LyndellBassell Industries) and 0.12 Kg ethylene-methacrylate copolymer(Lotryl 20 MA08, Arkema) and extruded through a twin screw extruder(Prism TS24E, ThermoFisher) at 240° C. The extrudate was cooled withwater and then pelletised. The pellets were dried at 110° C. for 3hours, then injection moulded into articles having dimensions of 125 mmlong, 12.5 mm wide and 3.2 mm thick using an injection moulding machine(Boy 22S, BOYS Machines) at 240° C.

Example 9—Elution Test of Articles Comprising an Aromatic Tracer inSynthetic Oil

A sample (0.5666 g) of the article from Example 8 was tested in thesynthetic oil described in Example 6 following the procedure of Example6.

The elution profile of tracer from the article from Example 8 is shownin FIG. 5. The release of tracer from the article containingmicroencapsulated tracer in Example 8 was slower than the release oftracer from articles where the tracer was not microencapsulated, asshown in Comparative examples 7 and 8, described in the followingsections. The release of tracer from the article containingmicroencapsulated tracer had an initial release of about 20% of theapplied tracer, followed by a slower, approximately linear release ofless than about 30% of the applied tracer over the next approximately 40days. The release rate over the linear release phase was less than about0.75% per day over the about 40 days (<30%/40 days).

Example 10—Elution Test of Sustained Release Cylinder in a Synthetic Oil

A cylinder made in Example 2 containing a microencapsulated haloaromatictracer was tested in synthetic oil following the procedure of Example 6.The elution profile is shown in FIG. 6. The release of tracer from thearticle was much slower than that observed even from other articlescontaining microencapsulated tracer as shown by the release of less than0.08% of the initial amount of tracer over a period of about 5000 hours(about 200 days). Extrapolation of this data indicates that under theconditions of this test, a sustained, measureable release of tracer canbe expected to last at least about 5 years, preferably at least about 10years, more preferably at least about 15 years, and most preferably atleast about 20 years.

Example 11—Microencapsulation of a Liquid Tracer

An oil tracer (Tracer D: A liquid benzene tracer substituted with mixedhalogens, density 2.0 g/cm³ at 25° C. and 1 atm) was encapsulated asdescribed below. 1.52 g carboxylmethylcellulose sodium salt (Sigma) wasdissolved in 81.8 g water and then mixed with 18.63 g Beetle resin (BIP)and 0.36 g formic acid (96%, Sigma) to form an aqueous mixture. Theaqueous mixture was stirred at 25° C. for 1 hour. 0.57 g Narad SolventRed 175 dye was dissolved in 60 g of the liquid tracer. The liquidtracer/dye mixture and the aqueous mixture were then homogenisedtogether for 5 minutes using a Silverson L4R laboratory homogeniser.During the homogenisation process, 120 g water was added to dilute themixture. The homogenised mixture was stirred at 25° C. for 2 hours andthen at 65° C. for 2 more hours. The resultant dispersion was filtered,dried in the air for 3 days and then dried in a vacuum oven at 40° C.for 10 hours. The dried powder product containing the encapsulatedtracer was filtered through a 425 μm sieve.

Example 12—Preparation of Slow Release Articles with MicroencapsulatedLiquid Oil Tracer

A mixture of 10 g solid powder of microencapsulated liquid oil tracerfrom Example 11, 9 g bisphenol A diglycidyl ether (Sigma) and 1 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cylindrical shape with a radius of 0.9 cm and aheight of 1.1 cm. The moulded composition was cured in an oven at 60° C.for 2 hours. The articles in the shape of a cylinder were easily peeledoff from the moulds. The articles contained 41% by weight of liquidtracer D. The cylinder appeared to be uniform throughout and had a veryslightly purplish red colour coming from dyes dosed in the liquidtracer.

Example 13—Microencapsulation of a Biocide

A biocide (Biocide A: an anthraquinone compound, density ˜1.3 g/cm3 at25° C. and 1 atm) was encapsulated as described below. 1.2 gcarboxylmethylcellulose sodium salt (Sigma) was dissolved in 78.3 gwater and then mixed with 15.9 g Beetle resin (BIP) and 0.35 g formicacid (96%, Sigma) to form an aqueous mixture. The aqueous mixture wasstirred at 25° C. for 1 hour. 60 g of the biocide and the aqueousmixture were then homogenised together for 5 minutes using a SilversonL4R laboratory homogeniser. During the homogenisation process, 300 gwater was added to dilute the mixture. The homogenised mixture wasstirred at 25° C. for 2 hours and then at 65° C. for 2 more hours. Theresultant dispersion was filtered, dried in the air for 3 days and thendried in a vacuum oven at 50° C. for 8 hours. Total biocide content inthe final powder product was 85%. The dried powder product containingthe encapsulated biocide was filtered through a 425 μm sieve.

Example 14—Preparation of an Article with a Microencapsulated Biocide

A mixture of 10 g microencapsulated biocide particles obtained fromExample 13, 9 g bisphenol A diglycidyl ether (Sigma) and 1 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cylindrical shape with a radius of 0.9 cm and aheight of 1.1 cm. The moulded composition was cured in an oven at 60° C.for 2 hours. The articles in the shape of a cylinder were easily removedfrom the moulds. The cylinder contained 41% by weight of biocide A. Thecylinder appeared to be uniform throughout and had a very slightlyyellow colour.

Example 15—Preparation of an Article with Microencapsulated Tracer B

A mixture of 10 g microencapsulated tracer B particles obtained fromExample 4, 9 g bisphenol A diglycidyl ether (Sigma) and 1 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cylindrical shape with a radius of 0.9 cm and aheight of 1.1 cm. The moulded composition was cured in an oven at 60° C.for 2 hours. The articles in the shape of a cylinder were easily removedfrom the moulds. The cylinder contained 41% by weight of tracer B. Thecylinder appeared to be uniform throughout and had only a very slightlyoff-white colour.

Example 16—Preparation of an Article with Microencapsulated Tracer C

A mixture of 10 g microencapsulated tracer C particles obtained fromExample 7, 9 g bisphenol A diglycidyl ether (Sigma) and 1 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cylindrical shape with a radius of 0.9 cm and aheight of 1.1 cm. The moulded composition was cured in an oven at 60° C.for 2 hours. The articles in the shape of a cylinder were easily removedfrom the moulds. The cylinder contained 41% by weight of tracer C. Thecylinder appeared to be uniform throughout and had a slightly creamwhite colour.

Comparative Example 1—Preparation of an Article Comprising an AromaticTracer that is not Microencapsulated

Solid aromatic tracer A was ground and sieved through a 100 μm sieve.8.2 g of the sieved tracer, 10.51 g bisphenol A diglycidyl ether (Sigma)and 1.17 g triethylenetetramine (technical grade, Sigma) were mixedtogether, moulded into the form of a cylinder and cured following theprocedure as described in Example 2. The cylinder contained 40% byweight of tracer A. The cylinder obtained was not uniform in appearancealong the depth of the cylinder. Accumulation of the tracer at thebottom of the cylinder was noticed. The top of the cylinder wastransparent while the bottom was opaque, due to settling of the tracerin the polymer. The cylinder became more opaque towards the bottom. Theentire cylinder had a strong yellow colour.

Comparative Example 2—Elution Test of an Aromatic Tracer that is notMicroencapsulated from an Article into Toluene

An article in the form of a cylinder made from Comparative Example 1(mass: 3.2721 g) was tested to determine its elution properties intotoluene using the same setup and following the procedure as outlined inExample 3. The cylinder showed very poor integrity. Big cracks appearedthroughout the cylinder within 120 hours of being left in toluene at 60°C.

The elution profile of tracer that was not microencapsulated from thecylinder of Comparative Example 1 is shown in FIG. 3. The release of thetracer is rapid and not sustained. About 70% of the tracer was releasedin the first 7 days (˜150 mg every 24 hours) and another 22% released in˜4 weeks of time gradually (in average 10 mg every 24 hours). Afterthese two elution periods, the release slowed and nearly stopped.

Comparative Example 3—Preparation of a Tracer that is notMicroencapsulated from an Article Comprising Fumed Silica

Solid aromatic tracer A was ground and sieved through a 100 μm sieve.8.2 g of the sieved tracer particles, 10.09 g bisphenol A diglycidylether (Sigma), 1.12 g triethylenetetramine (technical grade, Sigma) and0.47 g fumed silica (Sigma) were mixed together, moulded and curedfollowing the procedure described in Example 2. The cylinder contained40% by weight of tracer A. The cylinder obtained was more uniform thanthe cylinder of Comparative Example 1, but was still not uniform alongthe depth of the cylinder. A slight accumulation of tracer on the bottomof the cylinder was observed. The top of the cylinder was slightlytransparent while the bottom was opaque with light yellow colour, due tosettling of tracers in the polymer. The cylinder became gradually moreopaque from the top to the bottom. The cylinder had a slight yellowcolour.

Comparative Example 4—Elution Test of an Aromatic Tracer that is notMicroencapsulated from an Article Comprising Fumed Silica into Toluene

An article in the form of a cylinder made from the material inComparative Example 3 (mass: 3.3396 g) was tested for elution propertiesinto toluene using the same setup and following the procedure asoutlined in Example 3. The cylinder showed poor integrity. Big cracksappeared throughout the cylinder within 330 hours of being place intoluene at 60° C.

The elution profile of the tracer that is not microencapsulated from thecylinder of Comparative Example 3 is shown in FIG. 3. Compared to thesimple mixture of tracer that is not microencapsulated and epoxy resinin Comparative Example 1, the release of tracer from the sample intoluene from Comparative Example 3 was improved, but was still fairlyrapid, with about 35% of the tracer having been released in the first 2days (˜230 mg every 24 hours) and the remaining tracer being released injust over a 3 month period (average ˜9.5 mg every 24 hours).

Comparative Example 5—Preparation of an Article Comprising an AromaticKetone Tracer that is not Microencapsulated

Solid aromatic ketone tracer B was ground and sieved through a 100 μmsieve. 0.4 Kg tracer (not microencapsulated), 1.52 Kg polybutyleneterephthalate (Arnite T08 200 DSM) and 80 g ethylene-methacrylatecopolymer (Lotryl 20 MA08, Arkema) were compounded and injection mouldedfollowing the procedure as outlined in Example 5.

Comparative Example 6—Elution Test of an Aromatic Ketone Tracer that isnot Microencapsulated from an Article into a Synthetic Oil

An article made from Comparative Example 5 (mass: 0.7366 g) was testedin the synthetic oil as described in Example 6 and following theprocedure as outlined in Example 6.

The elution profile of tracer that is not microencapsulated from thecylinder from Comparative Example 5 is shown in FIG. 4. Tracer that wasnot microencapsulated was released from the article much faster thanmicroencapsulated tracer prior to incorporation in polybutyleneterephthalate as described in Example 4-5-6. About 75% of the tracer wasreleased over the first 8 days and about 10% of the tracer was releasedfrom about 8 to 49 days.

Comparative Example 7—Preparation of an Article Comprising an AromaticTracer that is not Microencapsulated

Solid aromatic tracer C was ground and sieved through a 100 μm sieve.0.4 Kg of the tracer (not microencapsulated), 1.52 Kg isotacticpolypropylene (Moplen HP556E LyndellBassell Industries) and 80 gethylene-methacrylate copolymer (Lotryl 20 MA08, Arkema) were compoundedand injection moulded following the procedure as outlined in Example 5.

Comparative Example 8—Elution Test of a Tracer that is notMicroencapsulated from an Article into a Synthetic Oil

An article made from Comparative Example 7 (mass: 0.8348 g) was testedin synthetic oil using the procedure described in Example 6.

The elution profile of tracer that was not microencapsulated from thecylinder of Comparative Example 7 is shown in FIG. 5. The tracer thatwas not microencapsulated was released from the article much faster thana comparable article in which the tracer was microencapsulated prior toincorporation in polypropylene as described in Examples 7-8-9. By 12days, about 50% of the total amount of tracer was released from thearticle of Comparative Example 7, where the tracer was notmicroencapsulated, while this amount of tracer was not released from thecomparable article having microencapsulated tracer until about 42 days.The release of tracer that was not microencapsulated from the article ofComparative Example 7 had an initial release of about 20% of the applieddose over the first day, followed by a linear release from days 1 to 14,where the total release of the tracer was from about 20% to about 55% ofthe total tracer loading, and then a third, slower, approximately linearrelease where the total release of the tracer was from about 55% toabout 85% of the total tracer loading from about 14 to about 49 days.

Comparative Example 9—Preparation of an Article Comprising Tracer B thatis not Microencapsulated

Solid tracer B was ground and sieved through a 100 μm sieve. 8.2 g ofthe sieved tracer, 10.51 g bisphenol A diglycidyl ether (Sigma) and 1.17g triethylenetetramine (technical grade, Sigma) were mixed together,moulded into the form of a cylinder and cured following the procedure asdescribed in Example 2. The cylinder was quite uniform throughout andhad a slight off-white colour.

Comparative Example 10—Preparation of an Article Comprising Tracer Cthat is not Microencapsulated

Solid tracer C was ground and sieved through a 100 μm sieve. 8.2 g ofthe sieved tracer, 10.51 g bisphenol A diglycidyl ether (Sigma) and 1.17g triethylenetetramine (technical grade, Sigma) were mixed together,moulded into the form of a cylinder and cured following the procedure asdescribed in Example 2. The cylinder contained 40% by weight of tracerC. The cylinder obtained was not uniform along the depth of thecylinder, with accumulation of tracer at the bottom of the cylinderbeing observed. The top of the cylinder had a very light yellow colourwhile the bottom of the cylinder had a quite strong yellow colour. Thecolour became darker as the bottom was approached.

Comparative Example 11—Preparation of an Article Comprising Biocide Athat is not Microencapsulated

8.2 g of biocide A that was not microencapsulated, 10.51 g bisphenol Adiglycidyl ether (Sigma) and 1.17 g triethylenetetramine (technicalgrade, Sigma) were mixed together, moulded into the form of a cylinderand cured following the procedure as described in Example 2. Thecylinder contained 40% by weight of biocide. The cylinder obtained wasnot uniform along the depth of the cylinder, with accumulation ofbiocide at the bottom of the cylinder being observed. The top of thecylinder had a very dark yellow colour and the bottom side had an evendarker yellow colour, with the darkness of the colour increasing as thebottom was approached.

Comparative Example 12—Preparation of an Article Comprising LiquidTracer D that is not Microencapsulated

8.2 g of liquid tracer D that was not microencapsulated, 10.51 gbisphenol A diglycidyl ether (Sigma) and 1.17 g triethylenetetramine(technical grade, Sigma) were mixed together, then poured into the samemould as described in Example 2. The moulded composition was placed inan oven at 60° C. for 2 hours to cure. After 2 hours, a solid cylinderhad not been formed.

Example 17—Elution Test of Sustained Release Articles ContainingMicroencapsulated Aromatic Oil Tracer B in a Synthetic Oil

A synthetic oil composed of 80% Transulate transformer oil (Smith &Allan) and 20% Downtherm Q oil (Dow) was used as a model oil to test theelution performance of the sustained release article. A cylinder article(3.7556 g) containing microencapsulated aromatic tracer B made fromExample 15 was suspended in a glass bottle containing 200 mL of theabove mentioned synthetic oil. The solution of synthetic oil and thecylinder was stirred at a temperature of 90° C. The procedures fortaking samples and changing oils were similar to that described inExample 3.

The elution profile of the microencapsulated tracer based test piecesfrom Example 15 is shown in FIG. 7. The release of the tracer from thearticle comprising the microencapsulated tracer B was sustained comparedto the release of tracer that was not microencapsulated as shown inComparative Example 13 described below. The compositions containingmicroencapsulated tracer released just less than 1% of the initialamount of tracer present over 6 days, while Comparative Example 13released about 90% of the initial amount of tracer in the same period oftime.

Example 18—Extended Elution Test of Aromatic Oil Tracer A from SustainedRelease Articles into Toluene

Toluene was used as a model oil for characterising the elution of tracerfrom articles in the shape of cylinders. After over 4000 hours elutiontest in toluene in Example 3, the same cylinder was subjected toextended elution test continuously in toluene at 60° C., following theprocedure described in Example 3.

The elution profile of tracer from the extended is shown in FIG. 8. Itis clear that the composition prepared in Example 2 continued to providefor a sustained release with an overall linear release of the tracerbeyond the initial 4000 hours' period described in Example 3 to 16200hours (˜22 months). About 40% of the applied tracer had been releasedbetween 4000 and 16200 hours.

Example 19—Microencapsulation of a Fifth Oil Tracer

A fifth oil tracer (Tracer E: a solid aromatic tracer, density 2.6 g/cm3at 25° C. and 1 atm) was used without any grinding. 0.48 gcarboxylmethylcellulose sodium salt (Sigma) was dissolved in 100 g waterand then mixed with 6.36 g Beetle resin (BIP) and 0.14 g formic acid(96%, Sigma) to form an aqueous mixture. The aqueous mixture was stirredat 25° C. for 1 hour.

100 g of the sieved tracer and the aqueous mixture were then homogenisedtogether for 15 minutes using a Silverson L4R laboratory homogeniser.The homogenised mixture was stirred at 25° C. for 2 hours and then at65° C. for 2 more hours. The resultant dispersion was filtered, dried inthe air for 24 hours and then dried in a vacuum oven at 50° C. for 8hours. The dried powder product was filtered through a 800 μm sieve.Total tracer content in the final powder product was 95.2%.

Example 20—Preparation of Sustained Release Articles withMicroencapsulated Oil Tracer E

A mixture of 11.0 g microencapsulated oil tracer particles obtained fromExample 19, 10.0 g bisphenol A diglycidyl ether (Sigma), and 1.0 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cube shape with edge length of 1.5 cm. The mouldedcomposition was cured in an oven at 60° C. for 2 hours. The articles inthe shape of a cube were easily removed from the moulds. The articlescontained 47.6% by weight of tracer E. The cubes appeared to be uniformthroughout and showed only an off-white colour.

Example 21—Preparation of Sustained Release Articles withMicroencapsulated Oil Tracer E

A mixture of 8.5 g microencapsulated oil tracer particles obtained fromExample 19 with 5.0 g formulated epoxy resin I, comprised of 4.0 gbisphenol A diglycidyl ether (Sigma) and 1.0 g epoxy compound, and 1.0 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cube shape with edge length of 1.5 cm. The mouldedcomposition was cured in an oven at 60° C. for 2 hours. The articles inthe shape of a cube were easily removed from the moulds. The articlescontained 55.8% by weight of tracer E. The cubes appeared to be uniformthroughout and showed only an off-white colour.

Example 22—Preparation of Sustained Release Articles withMicroencapsulated Oil Tracer E

A mixture of 8.5 g microencapsulated oil tracer particles obtained fromExample 19 with 5.0 g formulated epoxy resin II, comprised of 3.50 gbisphenol A diglycidyl ether (Sigma) and 1.5 g epoxy compound, and 1.0 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cube shape with edge length of 1.5 cm. The mouldedcomposition was cured in an oven at 60° C. for 2 hours. The articles inthe shape of a cube were easily removed from the moulds. The articlescontained 55.8% by weight of tracer E. The cubes appeared to be uniformthroughout and showed only an off-white colour.

Example 23—Elution Test of Sustained Release Cube in a Synthetic Oil

A cube made in Example 20 containing microencapsulated aromatic tracer Ewas tested in synthetic oil following the procedure of Example 17. Theelution profile is shown in FIG. 9. The release of tracer from thearticle was very slow but steady and sustained. Only less than 0.03% ofthe tracer was released within 26 days of elution. This is remarkablyslower than the release of tracer E which was not microencapsulated asdescribed in Comparative Example 14 and 15 below. The article comprisingpure tracer E made in Comparative Examples 14 released about 28% of theinitial amount of the tracer in 26 days (Comparative Example 15).

Example 24—Elution Test of Sustained Release Cube in a Synthetic Oil

A cube made in Example 21 containing microencapsulated aromatic tracer Ewas tested in synthetic oil following the procedure of Example 17. Theelution profile is shown in FIG. 10. Less than 1.5% of the tracer wasreleased within 5 months of elution. The release of tracer from thearticle was steady, slow and sustained, but faster than using purebisphenol A diglycidyl and triethylenetetramine as the bulk polymer(Example 20 and 23).

Example 25—Elution Test of Sustained Release Cube in a Synthetic Oil

A cube made in Example 22 containing microencapsulated Aromatic tracer Ewas tested in synthetic oil following the procedure of Example 17. Theelution profile is also shown in FIG. 10. Less than 5.5% of the tracerwas released within 5 months of elution. The release of tracer from thearticle was steady, slow and sustained, but much faster both than usingpure bisphenol A diglycidyl ether and triethylenetetramine as the bulkpolymer (Example 20 and 23) and using formulated epoxy resin I as bulkpolymer.

Comparative Example 13—Elution Test of Aromatic Oil Tracer B that is notMicroencapsulated from an Article into a Synthetic Oil

An article made from Comparative Example 9 (mass: 3.7590 g) was testedin synthetic oil using the procedure described in Example 17.

The elution profile of tracer B that was not microencapsulated from thecylinder of Comparative Example 9 is shown in FIG. 11. The release ofthe tracer from the article comprising the tracer B that was notmicroencapsulated was very fast and not sustained compared to therelease of tracer that was microencapsulated as shown in Example 17described above. The article made in Comparative Examples 9 releasedabout 90% in 6 days. The compositions containing microencapsulatedtracer released just less than 1% of the initial amount of tracerpresent within the same period of time (Example 17).

Comparative Example 14—Preparation of Release Articles with Oil Tracer Ethat is not Microencapsulated

Oil tracer E was used without any grinding. A mixture of 10.0 g tracer Eparticles, 10.0 g bisphenol A diglycidyl ether (Sigma), and 1.0 gtriethylenetetramine (technical grade, Sigma) were combined in a plasticcontainer and mixed with a stainless steel spatula. The mixture wastransferred to a 25 mL plastic syringe and injected into silicon moulds.The moulds were in a cube shape with edge length of 1.5 cm. The mouldedcomposition was cured in an oven at 60° C. for 2 hours. The articles inthe shape of a cube were easily removed from the moulds. The articlescontained 47.6% by weight of tracer E. The cylinder showed an off-whitecolour.

Comparative Example 15—Elution Test of Aromatic Oil Tracer E that is notMicroencapsulated from an Article into a Synthetic Oil

An article made from Comparative Example 14 (mass: 5.1840 g) was testedin synthetic oil using the procedure described in Example 17.

The elution profile of tracer E that was not microencapsulated from thecube of Comparative Example 14 is shown in FIG. 12. The release of thetracer from the article comprising the tracer E that was notmicroencapsulated was fast compared to the release of tracer that wasmicroencapsulated as shown in Examples 21 and 23 described above. Thearticle made in Comparative Examples 14 released about 28% in 26 days.The compositions containing microencapsulated tracer in Example 21 and23 released just less than 0.03% of the initial amount of tracer presentwithin 26 days.

Although the invention is illustrated and described herein withreference to specific aspects of the invention, the invention is notintended to be limited to the details shown. Rather, variousmodifications can be made in the details within the scope and range ofequivalents of the claims and without departing from the invention.

What is claimed is:
 1. A composition comprising: (a) microcapsulescomprising an oil field chemical and a microencapsulant, where themicrocapsules have an outer surface, and the oil field chemical iscontained within the microcapsules, and (b) a bulk polymer, where themicrocapsules are embedded within the bulk polymer.
 2. The compositionof claim 1, where the microcapsule comprises: a core shell structurecomprising: (a) a core comprising at least one oil field chemical and(b) a shell comprising a polymeric microencapsulant.
 3. The compositionof claim 1, where the microcapsule comprises a core multi-shellstructure comprising: (a) a core comprising at least one oil fieldchemical, (b) a first shell comprising a polymeric microencapsulantlocated adjacent to the core; and (c) one or more additional shellslocated over the first shell, each additional shell comprising apolymeric microencapsulant that is different than the polymericmicroencapsulant in an adjacent shell.
 4. The composition of claim 1,where the microcapsule comprises a multi-core shell structurecomprising: (a) a core comprising a plurality of sub-cores, where eachsub-core comprises at least one oil field chemical, and the sub-coresare dispersed in a non-polymeric compound, and (b) a shell comprising apolymeric microencapsulant.
 5. The composition of claim 1, where themicrocapsule comprises a micro-matrix structure comprising a corecomprising at least one oil field chemical entrapped within amicro-matrix comprising a polymeric microencapsulant.
 6. The compositionof claim 1, where the microcapsule comprises a micro-matrix with shellstructure comprising: (a) a core comprising at least one oil fieldchemical entrapped within a micro-matrix comprising a polymericmicroencapsulant; and (b) a shell comprising a polymericmicroencapsulant.
 7. The composition of claim 1, where the microcapsulecomprises a multi-core-micro-matrix with shell structure comprising: (a)a micro-matrix comprising a plurality of sub-cores, where each sub-corecomprises at least one oil field chemical, and the sub-cores areentrapped within the micro-matrix, and (b) a shell comprising apolymeric microencapsulant.
 8. The composition of claim 1, where, whenthe microcapsules comprise two or more shells, each shell comprises apolymeric microencapsulant that is different than the polymericmicroencapsulant in an adjacent shell.
 9. The composition of claim 1,where, when the microcapsule comprises two or more shells, one or moreshells comprise an additive or an oil field chemical.
 10. Thecomposition of claim 1, wherein the microencapsulant is amelamine-formaldehyde, a urea-formaldehyde, a phenol-formaldehyde resin,a melamine-phenol-formaldehyde resin, a furan-formaldehyde resin, anepoxy resin, a polyacrylate, a polyester, a polyurethane, a polyamide, apolyether, a polyimide, a polyolefin, polypropylene-polyethylenecopolymers, polystyrene, functionalized polystyrene derivatives,gelatin, a gelatin derivative, cellulose, a cellulose derivative, astarch, a starch derivative, a polyvinyl alcohol, anethylene-vinylacetate copolymer, an ethylene-maleic-anhydride copolymer,a styrene-maleic anhydride copolymer, a vinyl acetate-maleic anhydridecopolymer, a vinyl ether-maleic anhydride copolymer, a methyl vinylether-maleic anhydride copolymer, an octadecyl vinyl ether-maleicanhydride copolymer, a polyacrylamide, a polyacrylic acid, apolyvinylpyrrolidone, a polyvinylpyrrolidone based copolymer, apolyacrylate based copolymer, a polyacrylamide, or a polyacrylamidebased copolymer, and mixtures thereof.
 11. The composition of claim 1,where the microencapsulant comprises an inorganic material.
 12. Thecomposition of claim 1, where the bulk polymer is a thermosettingpolymer, a thermoplastic polymer, or a blend thereof.
 13. Thecomposition of claim 1, wherein the bulk polymer comprises apolyethylene, a polypropylene, a polyacrylate, an aliphatic polyamide, apolyurethane, a vinyl ester, an epoxy resin, or a polybutyleneterephthalate.
 14. The composition of claim 1, wherein the microcapsuleshave a volume weighted average particle size of between 0.05 μm and 600μm, inclusive.
 15. The composition of claim 1, wherein the outer surfaceof the microcapsule comprises one or more groups that are reactive withthe bulk polymer.
 16. The composition of claim 1, wherein thecomposition is in the form of an article configured for placement in ahydrocarbon reservoir.
 17. The composition of claim 1, where thecomposition releases <45% of the applied dose of tracer present in themicrocapsule over a period of 45 days at 60° C. in a fluid representingan oil field fluid.
 18. A hydrocarbon reservoir monitoring systemcomprising a composition of claim
 1. 19. A method of making acomposition of claim 1 comprising the steps of: (a) providing aplurality of microcapsules, each microcapsule comprising an oil fieldcompound and a polymeric microencapsulant, where the microcapsulecomprises a core shell structure, a core multishell structure, amulti-core shell structure, a micro-matrix structure, a micro-matrixwith shell structure or a multi-core-micro-matrix with shell structure,and (b) embedding the microcapsule particles within a bulk polymer. 20.A method of tracing fluid flow from a hydrocarbon reservoir comprisingthe steps of placing within a well penetrating said reservoir acomposition of claim 1, where the oil field chemical is a tracer,collecting one or more samples of fluids flowing from the well andanalysing said sample to determine at least one of: (a) the presence orabsence of the tracer and (b) the concentration of one or more tracersin fluids flowing from the well.